Three major output pathways from the KaiABC-based oscillator cooperate to generate robust circadian
            <i>kaiBC</i>
            expression in cyanobacteria

Taniguchi, Yasuhito; Takai, Naoki; Katayama, Mikio; Kondo, Takao; Oyama, Tokitaka

doi:10.1073/pnas.0909924107

Cited by 57 publications

(78 citation statements)

References 21 publications

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“…Although a recent study did not detect RpaA phosphorylation in the absence of SasA, those experiments were conducted using a strain induced to restore native levels of KaiC (11). Our observation that phosphorylated RpaA is present in the absence of SasA in vivo suggests that an alternative interaction partner of RpaA may help maintain residual gene expression rhythms from the kaiBC promoter in an sasA null (20), a hypothesis that is consistent with a network organization model for two-component systems in S. elongatus (24).…”

Section: Discussionmentioning

confidence: 83%

“…Because phosphorylated RpaA is postulated to reflect RpaA activity (10, 11), we investigated whether crm1 affects the in vivo phosphorylation state of RpaA in circadian and diurnal cycles. In WT cells, RpaA phosphorylation peaks at subjective dusk (8-12 h after light onset) and ebbs at subjective dawn (11,20). To examine the influence of a dark cue on the RpaA phosphorylation pattern, we compared replicate WT samples that were entrained to a 12-h LD cycle (12:12 LD) and either left in the light or transferred to the dark at subjective dusk and sampled every 3 h after last light.…”

Section: Resultsmentioning

confidence: 99%

“…The timing information from the circadian oscillator in cyanobacteria is proposed to be conveyed through at least three output pathways, one of which is the two-component SasA-RpaA system (20). According to recent models, CikA and LabA act as negative effectors and converge on RpaA, which functions as the master circadian regulator of transcription (20), and circadian regulation of RpaA activity is the result of opposing kinase activity of SasA and phosphatase activity of CikA (11).…”

Section: Discussionmentioning

confidence: 99%

“…According to recent models, CikA and LabA act as negative effectors and converge on RpaA, which functions as the master circadian regulator of transcription (20), and circadian regulation of RpaA activity is the result of opposing kinase activity of SasA and phosphatase activity of CikA (11). Deletion of rpaA has pleiotropic effects on transcript levels and physiology in S. elongatus.…”

Section: Discussionmentioning

confidence: 99%

“…The lack of bioluminescence reporter rhythms in an rpaA null background suggests a decoupling or insensitivity to the KaiC oscillations. RpaA activity is critical for sustaining the transcription/translation feedback loop of KaiBC expression (20); however, a recent study suggested that the response regulator RpaB, not RpaA, binds directly to the promoters of rhythmically regulated target genes, including kaiBC, and represses them (22 12 LD cycle and sampled every 3 h over 18 h. Samples were either maintained in LL or collected after entering dark at 11 h after onset of light. The overall RpaA phosphorylation level in LD is significantly lower after 1 h in dark compared with the 12-h LL sample, but the overall phosphorylation cycle remains substantially the same under both LL and LD conditions.…”

Section: Discussionmentioning

confidence: 99%

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An allele of the crm gene blocks cyanobacterial circadian rhythms

Boyd

Bordowitz

Bree

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The SasA-RpaA two-component system constitutes a key output pathway of the cyanobacterial Kai circadian oscillator. To date, rhythm of phycobilisome associated (rpaA) is the only gene other than kaiA, kaiB, and kaiC, which encode the oscillator itself, whose mutation causes completely arrhythmic gene expression. Here we report a unique transposon insertion allele in a small ORF located immediately upstream of rpaA in Synechococcus elongatus PCC 7942 termed crm (for circadian rhythmicity modulator), which results in arrhythmic promoter activity but does not affect steady-state levels of RpaA. The crm ORF complements the defect when expressed in trans, but only if it can be translated, suggesting that crm encodes a small protein. The crm1 insertion allele phenotypes are distinct from those of an rpaA null; crm1 mutants are able to grow in a light:dark cycle and have no detectable oscillations of KaiC phosphorylation, whereas low-amplitude KaiC phosphorylation rhythms persist in the absence of RpaA. Levels of phosphorylated RpaA in vivo measured over time are significantly altered compared with WT in the crm1 mutant as well as in the absence of KaiC. Taken together, these results are consistent with the hypothesis that the Crm polypeptide modulates a circadian-specific activity of RpaA.chronobiology | transcription regulation

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Section: Discussionmentioning

confidence: 83%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 3 more Smart Citations

An allele of the crm gene blocks cyanobacterial circadian rhythms

Boyd

Bordowitz

Bree

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Circadian Programmes in Cyanobacteria

Johnson

2011

Encyclopedia of Life Sciences

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Cyanobacteria are prokaryotes that express circadian (daily) rhythms. In rhythmic environments, the fitness of cyanobacteria is improved when this clock is operational and when its circadian period is similar to the period of the environmental cycle. In cyanobacteria, three key proteins (KaiA, KaiB and KaiC) form a core molecular clockwork that orchestrates global gene expression by modulating chromosomal topology. The three‐dimensional structures of these proteins have been determined. KaiA, KaiB and KaiC form a multiprotein nanomachine that can reconstitute a circadian oscillator in vitro , and this oscillator appears to function as a post‐translational oscillator (PTO) in vivo . Because this PTO regulates rhythmic transcription and translation, the entire circadian system comprises both the PTO and a transcriptional/translational feedback loop. Models of the complete in vivo system have important implications for our understanding of circadian clocks in higher organisms, including mammals. Key Concepts: Prokaryotic cyanobacteria have a circadian timekeeping system that enhances fitness. These cells exhibit pervasive circadian regulation of gene expression, possibly mediated by cyclic changes of chromosomal topology. A circadian rhythm of the phosphorylation of the central clock protein KaiC can be reconstituted in vitro with three proteins derived from cyanobacteria (KaiA, KaiB and KaiC) and ATP. KaiA, KaiB and KaiC are the only circadian clock proteins for which the 3‐D structure of full‐length proteins is known. Structural, biochemical and biophysical methods have been used to study the mechanism by which KaiC is rhythmically phosphorylated and dephosphorylated. Mathematical modelling that has been applied to the in vitro and in vivo systems indicate the existence of a core biochemical post‐translational oscillator (PTO) that controls a larger transcription/translation feedback loop (TTFL).

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How Light Resets Circadian Clocks

2014

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The daily revolutions of the earth around its axis are responsible for day and night and its annual orbit around the sun for the seasons with their fluctuations in day length. Most organisms have adapted to these diurnal and annual cycles. The strategies and mechanisms used are quite delicate and complicated.It came as a surprise that photosynthesis and many other processes are, however, additionally controlled by internal clocks. Thus, photosynthesis fluctuates not only during the daily light-dark cycle (=LD; see the List of Abbreviations and http://www.circadian.org/dictionary.html) but also when the plants are kept under LL and constant temperature (Hennessey and Field 1991). However, the period length (period for short) of this rhythmic event then deviates from exactly 24 h and is therefore called circadian (from Latin circa, about, and dies, day). If in the absence of LD and temperature cycles other 24 h time cues (also called zeitgeber, German for time giver) would control the rhythm, it should show an exact 24 h rhythm. This is not the case, demonstrating the endogenous nature of a clock that is locked to light signals (see Fig. 18.1). Spectrum of RhythmsEndogenous rhythms of organisms are not only tuned to the daily cycle of 24 h. The range of rhythms found in organisms covers ultradian (with periods of several hours to very short ones), circadian, and annual (with periods of about a year) rhythms. Other rhythms such as tidal, 14-day, and monthly ones cope with influences of the moon on the earth, mainly on the water movements of the oceans, and they are therefore found in organisms at the coasts and in the sea. Annual rhythms interact with the day-length changes during the year (see below). There are furthermore rhythms with periods covering several years. The following discussion of a "biological clock" is restricted to circadian rhythms. Even they are often not just composed of one clock type but form a "circadian system" consisting of two or more clocks with different prop- Function of Circadian ClocksThe term "clock" usually implies a time-measuring device or function. For instance, the day length (or night length) can be determined by an organism. Since day length is a function of the time of the year (long days in summer, short days in winter), it can be used to time certain events such as flowering or tuber formation of a plant or breeding of birds and mammals during the most appropriate season. These processes are denoted photoperiodism (see Chap. 19).However, a clock can also be used to set a certain temporal order. For instance, the circadian control of our sleepwake cycle ensures that we rise in the morning and fall asleep in the evening at a preferred time. Food intake and digestion are likewise controlled by this clock and gated to certain times of the day (Silver et al. 2011;Duguay and Cermakian 2009;Forsgren 1935). The circadian clock will time these events also under constant conditions. Furthermore, circadian clocks can serve as alarm clocks.

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Three major output pathways from the KaiABC-based oscillator cooperate to generate robust circadian kaiBC expression in cyanobacteria

Cited by 57 publications

References 21 publications

An allele of the crm gene blocks cyanobacterial circadian rhythms

An allele of the crm gene blocks cyanobacterial circadian rhythms

Circadian Programmes in Cyanobacteria

How Light Resets Circadian Clocks

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