Role of KaiC phosphorylation in the circadian clock system of Synechococcus elongatus PCC 7942

The kaiA, kaiB and kaiC genes encode the core components of the cyanobacterial circadian clock in Synechococcus elongatus PCC 7942. Rhythmic expression patterns of kaiA and of the kaiBC operon normally peak in synchrony. In some mutants the relative timing of peaks (phase relationship) between these transcription units is altered, but circadian rhythms persist robustly. In this study, the importance of the transcriptional timing of kai genes was examined. Expressing either kaiA or kaiBC from a heterologous promoter whose peak expression occurs 12 h out of phase from the norm, and thus 12 h out of phase from the other kai locus, did not affect the time required for one cycle (period) or phase of the circadian rhythm, as measured by bioluminescence reporters. Furthermore, the data confirm that specific cis elements within the promoters of the kai genes are not necessary to sustain clock function.

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Shift in Conformational Equilibrium Underlies the Oscillatory Phosphoryl Transfer Reaction in the Circadian Clock

Life ◽

10.3390/life11101058 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1058

Author(s):

Pyonghwa Kim ◽

Neha Thati ◽

Shreya Peshori ◽

Hye-In Jang ◽

Yong-Ick Kim

Keyword(s):

Circadian Clock ◽

Time Course ◽

Test Tube ◽

Phosphoryl Transfer ◽

Post Translational Modification ◽

Traditional Role ◽

Bond Forming ◽

Synechococcus Elongatus Pcc 7942 ◽

Pcc 7942

Oscillatory phosphorylation/dephosphorylation can be commonly found in a biological system as a means of signal transduction though its pivotal presence in the workings of circadian clocks has drawn significant interest: for example in a significant portion of the physiology of Synechococcus elongatus PCC 7942. The biological oscillatory reaction in the cyanobacterial circadian clock can be visualized through its reconstitution in a test tube by mixing three proteins—KaiA, KaiB and KaiC—with adenosine triphosphate and magnesium ions. Surprisingly, the oscillatory phosphorylation/dephosphorylation of the hexameric KaiC takes place spontaneously and almost indefinitely in a test tube as long as ATP is present. This autonomous post-translational modification is tightly regulated by the conformational change of the C-terminal peptide of KaiC called the “A-loop” between the exposed and the buried states, a process induced by the time-course binding events of KaiA and KaiB to KaiC. There are three putative hydrogen-bond forming residues of the A-loop that are important for stabilizing its buried conformation. Substituting the residues with alanine enabled us to observe KaiB’s role in dephosphorylating hyperphosphorylated KaiC, independent of KaiA’s effect. We found a novel role of KaiB that its binding to KaiC induces the A-loop toward its buried conformation, which in turn activates the autodephosphorylation of KaiC. In addition to its traditional role of sequestering KaiA, KaiB’s binding contributes to the robustness of cyclic KaiC phosphorylation by inhibiting it during the dephosphorylation phase, effectively shifting the equilibrium toward the correct phase of the clock.

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Studies on the role of HtpG in the tetrapyrrole biosynthesis pathway of the cyanobacterium Synechococcus elongatus PCC 7942

Biochemical and Biophysical Research Communications ◽

10.1016/j.bbrc.2006.10.144 ◽

2007 ◽

Vol 352 (1) ◽

pp. 36-41 ◽

Cited By ~ 27

Author(s):

Satoru Watanabe ◽

Toshiaki Kobayashi ◽

Masakazu Saito ◽

Masumi Sato ◽

Kaori Nimura-Matsune ◽

...

Keyword(s):

Synechococcus Elongatus ◽

Biosynthesis Pathway ◽

Tetrapyrrole Biosynthesis ◽

Synechococcus Elongatus Pcc 7942 ◽

Pcc 7942

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Role of calcium in acclimation of the cyanobacterium Synechococcus elongatus PCC 7942 to nitrogen starvation

Microbiology ◽

10.1099/mic.0.022251-0 ◽

2009 ◽

Vol 155 (1) ◽

pp. 25-34 ◽

Cited By ~ 34

Author(s):

Francisco Leganés ◽

Karl Forchhammer ◽

Francisca Fernández-Piñas

Keyword(s):

Nitrogen Starvation ◽

Transcriptional Regulator ◽

Synechococcus Elongatus ◽

Signal Suppression ◽

Intracellular Ca ◽

Step Down ◽

Synechococcus Elongatus Pcc 7942 ◽

Pcc 7120 ◽

Pcc 7942

A Ca2+ signal is required for the process of heterocyst differentiation in the filamentous diazotrophic cyanobacterium Anabaena sp. PCC 7120. This paper presents evidence that a transient increase in intracellular free Ca2+ is also involved in acclimation to nitrogen starvation in the unicellular non-diazotrophic cyanobacterium Synechococcus elongatus PCC 7942. The Ca2+ transient was triggered in response to nitrogen step-down or the addition of 2-oxoglutarate (2-OG), or its analogues 2,2-difluoropentanedioic acid (DFPA) and 2-methylenepentanedioic acid (2-MPA), to cells growing with combined nitrogen, suggesting that an increase in intracellular 2-OG levels precedes the Ca2+ transient. The signalling protein PII and the transcriptional regulator NtcA appear to be needed to trigger the signal. Suppression of the Ca2+ transient by the intracellular Ca2+ chelator N,N′-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis[N-[2-[(acetyloxy)methoxy]-2-oxoethyl]]-,bis[(acetyloxy)methyl] ester (BAPTA-AM) inhibited expression of the glnB and glnN genes, which are involved in acclimation to nitrogen starvation and transcriptionally activated by NtcA. BAPTA-AM treatment partially inhibited expression of the nblA gene, which is involved in phycobiliprotein degradation following nutrient starvation and is regulated by NtcA and NblR; in close agreement, BAPTA-AM treatment partially inhibited bleaching following nitrogen starvation. Taken together, the results presented here strongly suggest an involvement of a defined Ca2+ transient in acclimation of S. elongatus to nitrogen starvation through NtcA-dependent regulation.

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