Misplaced Pages

#980019

64-453: KaiB is a gene located in the highly-conserved kaiABC gene cluster of various cyanobacterial species. Along with KaiA and KaiC , KaiB plays a central role in operation of the cyanobacterial circadian clock. Discovery of the Kai genes marked the first-ever identification of a circadian oscillator in a prokaryotic species. Moreover, characterization of the cyanobacterial clock demonstrated

128-525: A speciation event (orthologs), or a duplication event (paralogs), or else a horizontal (or lateral) gene transfer event (xenologs). Homology among DNA, RNA, or proteins is typically inferred from their nucleotide or amino acid sequence similarity. Significant similarity is strong evidence that two sequences are related by evolutionary changes from a common ancestral sequence. Alignments of multiple sequences are used to indicate which regions of each sequence are homologous. The term "percent homology"

192-451: A 44 hour long-period clock mutant, C44a , with wild-type (WT) genomic DNA library in a plasmid vector allowed testing for “rescue clones” with a normal period of 25 hours. When the DNA library from this rescued clone was placed into a plasmid at the original site, C44a was found to be completely rescued. One single gene cluster, kaiABC , was found to be rhythmic in nature when the fragment of

256-467: A circadian fashion, generally falling into Class I (dusk-peaking) and Class II (dawn-peaking) categories depending on their specific function. The rhythmic expression of cyanobacterial genes is driven by oscillation in the phosphorylation state of the Kai oscillator and its interaction with various output mechanisms. The evolution of the three kai genes – kaiA , kaiB , and kaiC – remains an area of active study. Recent phylogenetic evidence suggests that

320-414: A genome have been diverging for the same length of time (since their common origin in the whole genome duplication). Ohnologues are also known to show greater association with cancers, dominant genetic disorders, and pathogenic copy number variations. Homologs resulting from horizontal gene transfer between two organisms are termed xenologs. Xenologs can have different functions if the new environment

384-608: A higher affinity for oxygen than adult hemoglobin. Function is not always conserved, however. Human angiogenin diverged from ribonuclease , for example, and while the two paralogs remain similar in tertiary structure, their functions within the cell are now quite different. It is often asserted that orthologs are more functionally similar than paralogs of similar divergence, but several papers have challenged this notion. Paralogs are often regulated differently, e.g. by having different tissue-specific expression patterns (see Hox genes). However, they can also be regulated differently on

448-467: A monomeric form of the protein. However, monomeric KaiB must undergo a radical change in tertiary structure to associate with KaiC, shifting from a so-called ground state conformation (gs-KaiB) to a fold-switched conformation (fs-KaiB) capable of binding to the KaiC B-loop. To date, KaiB is the only known metamorphic clock protein – a class of proteins capable of reversible fold-switching. Fs-KaiB has

512-583: A mutation in gene A (gene A1), producing a new species with genes A1 and B. Then in a separate speciation event, one environment will favor a mutation in gene B (gene B1) giving rise to a new species with genes A and B1. The descendants' genes A1 and B1 are paralogous to each other because they are homologs that are related via a duplication event in the last common ancestor of the two species. Additional classifications of paralogs include alloparalogs (out-paralogs) and symparalogs (in-paralogs). Alloparalogs are paralogs that evolved from gene duplications that preceded

576-690: A nucleus, prokaryotic cells must have a different mechanism of keeping circadian time. In 1998, Ishiura et al. determined that the KaiABC protein complex was responsible for the circadian negative feedback loop in Synechococcus by mapping 19 clock mutants to the genes for these three proteins.(3) An experiment by Nakajima et al., in 2005, was able to demonstrate the circadian oscillation of the Synechococcus KaiABC complex in vitro . They did this by adding KaiA , KaiB , KaiC , and ATP into

640-498: A prokaryotic species. Following these discoveries, chronobiologists set out to identify the molecular mechanisms governing operation of the cyanobacterial clock. Takao Kondo , Masahiro Ishiura, Susan Golden , Carl Johnson , and their colleagues used bacterial luciferase , a reporter for gene expression, on the gene psbAI to monitor the activity of this clock gene found in Synechococcus cyanobacteria. The transformation of

704-516: A role in entrainment of the cyanobacterial clock. Instead, identified input mechanisms rely on biochemical changes that track photosynthetic reactions performed by the cyanobacterium, reactions that exhibit rate increases proportional to ambient light intensity. CikA and LdpA, for example, sense the redox state of the intracellular environment and relay changes to the Kai oscillator. In addition, KaiA and KaiC appear to directly detect metabolites of photosynthesis – specifically quinone and ATP – and adjust

SECTION 10

#1732791467981

768-430: A single amino acid substitution on one of the aforementioned genes determined that Kai proteins play a significant role in the Synechococcus circadian clock. Initially, it was thought that a transcription-translation feedback loop was necessary in creating circadian rhythms so it was believed that kaiABC would have this function as well. However, it was later discovered that inhibition of kaiBC mRNA accumulation using

832-402: A test tube in the approximate ratio recorded in vivo . They then measured the levels of KaiC phosphorylation and found that it demonstrated circadian rhythmicity for three cycles without damping. This cycle was also temperature compensating. They also tested incubating mutant KaiC protein with KaiA, KaiB, and ATP. They found that the period of KaiC phosphorylation matched the intrinsic period of

896-560: A thioredoxin-like fold that closely resembles the N-terminus of SasA, and competitively displaces the kinase’s binding to KaiC. However, the conformation change from gs-KaiB to fs-KaiB occurs slowly, permitting SasA binding to KaiC and downstream activation of RpaA from midday – when the B-loop first becomes exposed - until dusk. As a result, phospho-RpaA accumulates as the day progresses and peaks near dusk, appropriately timing increases in

960-454: A transcription or translation inhibitor did not prevent the circadian cycling of kaiC phosphorylation. Thus, it is the case that cyanobacterial clock rhythmicity is independent of both transcription and translation. Additionally, experiments were conducted to test the self-sustainable oscillation of KaiC phosphorylation, which is important in the regulation of the kaiABC gene cluster. By incubating KaiC together with KaiA and KaiB, as well as ATP,

1024-591: Is composed of three functional domains : the N-terminal amplitude-amplifier domain, the central period-adjuster domain and the C-terminal clock-oscillator domain. The N-terminal domain of KaiA, from cyanobacteria, acts as a pseudo-receiver domain, but lacks the conserved aspartyl residue required for phosphotransfer in response regulators. The C-terminal domain is responsible for dimer formation, binding to KaiC, enhancing KaiC phosphorylation and generating

1088-484: Is highly dependent on glutamate and pH. Sometimes, large regions of chromosomes share gene content similar to other chromosomal regions within the same genome. They are well characterised in the human genome, where they have been used as evidence to support the 2R hypothesis . Sets of duplicated, triplicated and quadruplicated genes, with the related genes on different chromosomes, are deduced to be remnants from genome or chromosomal duplications. A set of paralogy regions

1152-451: Is involved in recombination and recombinational repair, most likely involving the stabilisation or processing of branched DNA molecules or blocked replication forks because of its genetic redundancy with RecG and RuvABC. The overall fold of the KaiA monomer is that of a four- helix bundle, which forms a dimer in the known structure . KaiA functions as a homodimer . Each monomer

1216-545: Is likely to display a greater divergence in the sequence of the orthologs being studied. Given their tremendous importance for biology and bioinformatics , orthologous genes have been organized in several specialized databases that provide tools to identify and analyze orthologous gene sequences. These resources employ approaches that can be generally classified into those that use heuristic analysis of all pairwise sequence comparisons, and those that use phylogenetic methods. Sequence comparison methods were first pioneered in

1280-421: Is much simpler than models for eukaryotic circadian rhythm generators, the principles are largely the same. In both systems the circadian period is dependent on the interactions between proteins within the cell, and when the genes for those proteins are mutated, the expressed period changes. (1)(2) This model of circadian rhythm generation also has implications for the study of circadian “evolutionary biology”. Given

1344-472: Is not to be confused with conservation in amino acid sequences, where the amino acid at a specific position has been substituted with a different one that has functionally equivalent physicochemical properties. Partial homology can occur where a segment of the compared sequences has a shared origin, while the rest does not. Such partial homology may result from a gene fusion event. Homologous sequences are orthologous if they are inferred to be descended from

SECTION 20

#1732791467981

1408-400: Is often used to mean "sequence similarity”, that is the percentage of identical residues ( percent identity ), or the percentage of residues conserved with similar physicochemical properties ( percent similarity ), e.g. leucine and isoleucine , is usually used to "quantify the homology." Based on the definition of homology specified above this terminology is incorrect since sequence similarity

1472-696: Is organized as a ring-shaped homohexamer. Each monomer component contains four essential structural motifs: a CI domain, a CII domain, a B-loop binding domain, and a tail that protrudes from the C-terminus known as the A-loop. Because the CI and CII domains are aligned in the KaiC hexamer, they are collectively referred to as the CI and CII rings. KaiC has both intrinsic autokinase and autophosphate activity, each of which can be modulated by KaiA and KaiB binding. In particular,

1536-536: Is restricted to a group of higher-order cyanobacteria. For example, while the Synechococcus and Prochlorococcus cyanobacterial genera are closely related, kaiA is absent in Prochlorococcus species. Cyanobacteria lacking kaiA demonstrate oscillations in gene expression and cell cycle progression, but these rhythms are not self-sustaining and rapidly disappear under constant conditions. Contrasting cyanobacterial species lacking kai genes, some members of

1600-412: Is the observation, homology is the conclusion. Sequences are either homologous or not. This involves that the term "percent homology" is a misnomer. As with morphological and anatomical structures, sequence similarity might occur because of convergent evolution , or, as with shorter sequences, by chance, meaning that they are not homologous. Homologous sequence regions are also called conserved . This

1664-420: Is together called a paralogon . Well-studied sets of paralogy regions include regions of human chromosome 2, 7, 12 and 17 containing Hox gene clusters, collagen genes, keratin genes and other duplicated genes, regions of human chromosomes 4, 5, 8 and 10 containing neuropeptide receptor genes, NK class homeobox genes and many more gene families , and parts of human chromosomes 13, 4, 5 and X containing

1728-464: Is vastly different for the horizontally moving gene. In general, though, xenologs typically have similar function in both organisms. The term was coined by Walter Fitch. Homoeologous (also spelled homeologous) chromosomes or parts of chromosomes are those brought together following inter-species hybridization and allopolyploidization to form a hybrid genome , and whose relationship was completely homologous in an ancestral species. In allopolyploids,

1792-511: The Legionella pneumophila oxidative and salt stress responses. The core cyanobacterial circadian oscillator, encoded by the kaiA , kaiB , and kaiC genes, regulates global patterns of gene expression and governs essential cellular processes including photosynthesis and cell division. Cyclic, sequential rhythms of KaiC phosphorylation and dephosphorylation constitute the oscillator’s timekeeping mechanism both in vivo and in vitro . KaiC

1856-532: The ParaHox genes and their neighbors. The Major histocompatibility complex (MHC) on human chromosome 6 has paralogy regions on chromosomes 1, 9 and 19. Much of the human genome seems to be assignable to paralogy regions. Ohnologous genes are paralogous genes that have originated by a process of whole-genome duplication . The name was first given in honour of Susumu Ohno by Ken Wolfe. Ohnologues are useful for evolutionary analysis because all ohnologues in

1920-709: The Synechococcus family express paralogs of kaiB and kaiC referred to as kaiC2 , kaiB2 , kaiC3 , and kaiB3 . The function this expanded set of clock genes remains speculative, but current evidence suggests these paralogs help to fine-tune a central circadian rhythm established by kaiA , kaiB1 , and kaiC1 . Orthologs of kaiB and kaiC genes have been identified in some species of Archaea and Pseudomonadota . Likely originating from lateral transfer, some of these orthologs – particularly in cases where kaiB and kaiC are coincident - have been tentatively implicated in rudimentary timekeeping mechanisms. Others play roles in strikingly divergent cellular processes, such as

1984-549: The circadian oscillations . The KaiA protein from Anabaena sp. (strain PCC 7120) lacks the N-terminal CheY-like domain. KaiB adopts an alpha-beta meander motif and is found to be a dimer or a tetramer . KaiC belongs to a larger family of proteins ; it performs autophosphorylation and acts as its own transcriptional repressor . It binds ATP . Due to the lack of a nucleus in these organisms, there

KaiB - Misplaced Pages Continue

2048-409: The kai genes emerged sequentially: kaiC nearly 3,800 Mya, kaiB between 3,500-2,3200 Mya, and kaiA most recently around 1,000 Mya. The fusion of kaiC and kaiB into an operon under the control of a single promoter occurred shortly after kaiB ’s appearance in the genome. While all three kai genes are independently required for sustained circadian rhythmicity in cyanobacteria, the kaiA gene

2112-551: The last common ancestor (LCA) of the species being compared. They result from the mutation of duplicated genes during separate speciation events. When descendants from the LCA share mutated homologs of the original duplicated genes then those genes are considered paralogs. As an example, in the LCA, one gene (gene A) may get duplicated to make a separate similar gene (gene B), those two genes will continue to get passed to subsequent generations. During speciation, one environment will favor

2176-399: The shared ancestor . Orthology is strictly defined in terms of ancestry. Given that the exact ancestry of genes in different organisms is difficult to ascertain due to gene duplication and genome rearrangement events, the strongest evidence that two similar genes are orthologous is usually found by carrying out phylogenetic analysis of the gene lineage. Orthologs often, but not always, have

2240-554: The A-loop, and in turn both promotes the autophosphatase activity of KaiC and inhibits its autokinase activity. Dephosphorylation of KaiC occurs in the subjective night, and proceeds in the reverse order of phosphorylation; Thr432 is dephosphorylated before Ser431. Ultimately, these circadian rhythms in KaiC phosphorylation governed by KaiA and KaiB binding create a post-translation oscillator that can interact with both input pathways to entrain to changing environmental conditions and output pathways to mediate transcriptional events. Though

2304-702: The COGs database in 1997. These methods have been extended and automated in twelve different databases the most advanced being AYbRAH Analyzing Yeasts by Reconstructing Ancestry of Homologs as well as these following databases right now. Tree-based phylogenetic approaches aim to distinguish speciation from gene duplication events by comparing gene trees with species trees, as implemented in databases and software tools such as: A third category of hybrid approaches uses both heuristic and phylogenetic methods to construct clusters and determine trees, for example: Paralogous genes are genes that are related via duplication events in

2368-633: The HoxA-D clusters being the best studied. Another example are the globin genes which encode myoglobin and hemoglobin and are considered to be ancient paralogs. Similarly, the four known classes of hemoglobins ( hemoglobin A , hemoglobin A2 , hemoglobin B , and hemoglobin F ) are paralogs of each other. While each of these proteins serves the same basic function of oxygen transport, they have already diverged slightly in function: fetal hemoglobin (hemoglobin F) has

2432-400: The Kai oscillator is capable of generating endogenous rhythms in phosphorylation, it does not directly influence gene expression; none of the Kai proteins possess DNA-binding domains. Instead, a two-component system consisting of SasA, a histidine kinase , and RpaA, a transcription factor, connect changes in KaiC phosphorylation to transcriptional events. SasA can bind to the exposed B-loop of

2496-456: The KaiC molecule upon phosphorylation of the Ser431 residue. This interaction drives SasA autophosphorylation and subsequent phosphotransfer to RpaA. Phospho-RpaA activates the expression of dusking-peaking (Class 1) genes and represses the expression of dawn-peaking (Class 2) genes. Conversely, unphosphorylated RpaA represses the expression of Class 1 genes. As a result, rhythmic phosphorylation of

2560-485: The cellular complexity to maintain persistent, temperature-compensated timekeeping. In addition, the widely supported "circadian- infradian rule" stipulated that cellular functions could only be coupled to a circadian oscillator in cells dividing only as fast as once in a 24-hour period. Prokaryotes, which often undergo cellular division multiple times in a single day, failed to meet this condition. Over time, mounting evidence began to challenge this assertion and supported

2624-834: The complex, KaiA enhances the phosphorylation status of kaiC. In contrast, the presence of kaiB in the complex decreases the phosphorylation status of kaiC, suggesting that kaiB acts by antagonising the interaction between kaiA and kaiC. The activity of KaiA activates kaiBC expression, while KaiC represses it. Also in the KaiC family is RadA/Sms, a highly conserved eubacterial protein that shares sequence similarity with both RecA strand transferase and lon protease . The RadA/Sms family are probable ATP-dependent proteases involved in both DNA repair and degradation of proteins, peptides , glycopeptides . They are classified in as non-peptidase homologues and unassigned peptidases in MEROPS peptidase family S16 (lon protease family, clan SJ). RadA/Sms

KaiB - Misplaced Pages Continue

2688-479: The course of the day - constitute an operon under the control of a single promoter and are transcribed as a polycistronic mRNA. By contrast, protein levels of KaiA, which lies under the control of an independent promoter, remain fairly across a 24-hour period. In addition, the phase of the Kai oscillator can be shifted in response to environmental changes. However, unlike phase-shifting mechanisms characterized in eukaryotic organisms, photopigments do not appear to play

2752-490: The cyanobacteria clock oscillates in vitro . Additionally, they hope to discover the adaptive significance of circadian rhythms using clock gene mutants of cyanobacteria. The Rust lab is researching how the interactions of proteins, neurotransmitters, and ion gradients produce the behavior of living cyanobacteria cells, using a combination of techniques such as advanced biochemical microscopy and mathematical modeling. KaiABC See also: bacterial circadian rhythms In

2816-411: The cyanobacterium with the corresponding mutant genome. These results led them to conclude that KaiC phosphorylation is the basis for circadian rhythm generation in Synechococcus. (2) Cyanobacteria are the simplest organisms that have been observed demonstrating circadian rhythms.(2)(3) The primitiveness and simplicity make the KaiC phosphorylation model invaluable to circadian rhythm research. While it

2880-480: The existence of a bacterial circadian rhythm . For example, discrete temporal separation of photosynthesis and nitrogen fixation observed in cyanobacteria suggested the existence of some mechanism of circadian control. Finally, in 1986 Tan-Chi Huang and colleagues discovered and characterized robust, 24-hour rhythms of nitrogen fixation in Synechococcus cyanobacteria, demonstrating circadian rhythmicity in

2944-453: The existence of transcription-independent, post-translational mechanisms of rhythm generation, challenging the universality of the transcription-translation feedback loop model of circadian rhythmicity. Circadian rhythms - endogenous, entrainable oscillations in biological processes with periods that roughly correspond to the 24-hour day – were once believed to be an exclusive property of eukaryotic lifeforms. Prokaryotes were thought to lack

3008-585: The expression of Class 1 genes. Moreover, this time-lag in KaiB binding delays the onset of autophosphatase activity in KaiC, contributing to the circadian period of the cyanobacterial oscillator. While rhythmicity in the KaiABC oscillator can be reconstituted in vitro , the clock is subject to various additional levels of regulation in vivo . For example, a stoichiometric ratio of clock components must be maintained to preserve rhythmicity. kaiB and kaiC – whose transcript and protein levels oscillate considerable over

3072-446: The given speciation event. In other words, alloparalogs are paralogs that evolved from duplication events that happened in the LCA of the organisms being compared. The example above is an example alloparalogy. Symparalogs are paralogs that evolved from gene duplication of paralogous genes in subsequent speciation events. From the example above, if the descendant with genes A1 and B underwent another speciation event where gene A1 duplicated,

3136-437: The homologous chromosomes within each parental sub-genome should pair faithfully during meiosis , leading to disomic inheritance; however in some allopolyploids, the homoeologous chromosomes of the parental genomes may be nearly as similar to one another as the homologous chromosomes, leading to tetrasomic inheritance (four chromosomes pairing at meiosis), intergenomic recombination , and reduced fertility. Gametology denotes

3200-526: The new species would have genes B, A1a, and A1b. In this example, genes A1a and A1b are symparalogs. Paralogous genes can shape the structure of whole genomes and thus explain genome evolution to a large extent. Examples include the Homeobox ( Hox ) genes in animals. These genes not only underwent gene duplications within chromosomes but also whole genome duplications . As a result, Hox genes in most vertebrates are clustered across multiple chromosomes with

3264-489: The phase of the oscillator accordingly. To date, KaiB has not been implicated in an input pathway capable of entraining the cyanobacterial clock. Both Dr. Carl Johnson’s lab at Vanderbilt University and Dr. Michael Rust’s lab at the University of Chicago have research efforts focused on the KaiABC complex. The Johnson lab, in collaboration with Dr. Hassane Mchaourab’s lab, focuses on using biophysical methods to explain how

SECTION 50

#1732791467981

3328-449: The phosphorylation and dephosphorylation of residues Ser431 and Thr432 in the CII ring drive circadian rhythms in the Kai oscillator. At the start of the subjective day, the Ser431 and Thr432 residues of the KaiC hexamer are unphosphorylated, and the A-loop domains of its constituent monomers are exposed. KaiA binds to the A-loop domain of KaiC, promoting autokinase activity. Phosphorylation of

3392-643: The plant Flu regulatory protein is present both in Arabidopsis (multicellular higher plant) and Chlamydomonas (single cell green algae). The Chlamydomonas version is more complex: it crosses the membrane twice rather than once, contains additional domains and undergoes alternative splicing. However, it can fully substitute the much simpler Arabidopsis protein, if transferred from algae to plant genome by means of genetic engineering . Significant sequence similarity and shared functional domains indicate that these two genes are orthologous genes, inherited from

3456-465: The plasmid responsible for rescue was sequenced. kaiABC is composed of three individual genes: kaiA , kaiB , and kaiC . Examination of rescue patterns in over 50 clock mutants showing either short periods, long periods or arrhythmia revealed restoration to WT phenotype in all mutants. Further sequencing revealed 19 total kaiABC specific mutants, 14 of which had mutations in kaiC , 3 in kaiA , and 2 in kaiB . The mutant phenotypes being all caused by

3520-459: The protein level. For instance, Bacillus subtilis encodes two paralogues of glutamate dehydrogenase : GudB is constitutively transcribed whereas RocG is tightly regulated. In their active, oligomeric states, both enzymes show similar enzymatic rates. However, swaps of enzymes and promoters cause severe fitness losses, thus indicating promoter–enzyme coevolution. Characterization of the proteins shows that, compared to RocG, GudB's enzymatic activity

3584-422: The protein occurs in an ordered, sequential manner – Thr432 is phosphorylated first, followed by Ser431. Phosphorylation of the Ser431 residue drives a significant conformational change in the KaiC hexamer. The CI and CII rings of the protein complex stack more tightly, exposing the previously occluded B-loop. The B-loop in turn recruits KaiB, which simultaneously binds to KaiA and KaiC. KaiB binding removes KaiA from

3648-452: The same ancestral sequence separated by a speciation event: when a species diverges into two separate species, the copies of a single gene in the two resulting species are said to be orthologous. Orthologs, or orthologous genes, are genes in different species that originated by vertical descent from a single gene of the last common ancestor . The term "ortholog" was coined in 1970 by the molecular evolutionist Walter Fitch . For instance,

3712-423: The same function. Orthologous sequences provide useful information in taxonomic classification and phylogenetic studies of organisms. The pattern of genetic divergence can be used to trace the relatedness of organisms. Two organisms that are very closely related are likely to display very similar DNA sequences between two orthologs. Conversely, an organism that is further removed evolutionarily from another organism

3776-472: The simplicity of cyanobacteria and of this circadian system, it may be safe to assume that eukaryotic circadian oscillators are derived from a system similar to that present in cyanobacterium. (1) Paralogs Sequence homology is the biological homology between DNA , RNA , or protein sequences , defined in terms of shared ancestry in the evolutionary history of life . Two segments of DNA can have shared ancestry because of three phenomena: either

3840-615: The temperature compensation aspect of the KaiABC clock was proved. Additionally, such circadian periods seen in kaiC in vivo mutants were also observed in in vitro strains. Cyanobacteria are a group of photosynthetic, nitrogen-fixing bacteria that are known to be one of the first life forms on Earth, and are thought to have emerged at least 3,500 million years ago (Mya). They are the only known oxidative photosynthetic prokaryotes. Cyanobacteria use circadian clocks to regulate nitrogen-fixation, cell division, and other metabolic processes. The vast majority of cyanobacterial genes are expressed in

3904-549: The transcription factor, driven by the Kai oscillator and associated SasA activity, produces rhythmic patterns in gene expression. KaiB serves as a major regulator of the SasA-RpaA pathway, and exhibits structural adaptations that both contribute to circadian rhythm generation and facilitate interaction with SasA and KaiC. The majority of KaiB expressed in cyanobacteria exists as an inactive homotetramer, incapable of interacting with KaiC. The KaiB tetramer exists in equilibrium with

SECTION 60

#1732791467981

3968-434: The two groups oscillated with opposite phases. This led them to conclude that the Synechococcus sp. genome was regulated by a circadian clock. (1) The circadian oscillators in eukaryotes that have been studied function using a negative feedback loop in which proteins inhibit their own transcription in a cycle that takes approximately 24 hours. This is known as a transcription-translation-derived oscillator (TTO).(2) Without

4032-428: Was doubt as to whether or not cyanobacteria would be able to express circadian rhythms. Kondo et al. were the first to definitively demonstrate that cyanobacteria do in fact have circadian rhythms. In a 1993 experiment, they used a luciferase reporter inserted into the genetically tractable Synechococcus sp., which was grown in a 12:12 light-dark cycle to ensure “entrainment”. There were two sets of bacteria so that one

4096-416: Was in light while the other was in darkness during this entrainment period. Once the bacteria entered the stationary phase, they were transferred into test tubes kept in constant light, except for 5-minute recording periods every 30 minutes, in which the tubes were kept in darkness to measure their levels of bioluminescence . They found that the level of bioluminescence cycled at a near 24-hour period, and that

#980019