1887

Abstract

KaiA KaiB and KaiC are essential circadian clock proteins in the unicellular cyanobacterium PCC 7942. KaiA protein activates transcription of the operon, which is believed to be a crucial step in the oscillating feedback loop of cyanobacteria. In this study, ∼∼400 mutations were introduced into by PCR-based mutagenesis, and rhythmic phenotypes of these mutants were studied by a bioluminescence reporter. In contrast to mutations in KaiB or KaiC, the vast majority of KaiA mutations extended the period and only rarely shortened it. The period could be extended to 35 h without lowering the mean or peak levels of expression. However, several mutations resulted in low-amplitude oscillations or arrhythmia, which were accompanied by lowered transcription. These results imply that the KaiA protein can change the period length of the circadian rhythm directly (through an unknown biochemical mechanism) or indirectly (by lowering expression). Specific mutations of KaiA were identified in 34 mutants. While mutations mapped to various locations of the KaiA sequence, two clusters of period-altering mutations were found. This suggested that these regions are important domains of the KaiA protein for defining the period length. On the other hand, different sequences within KaiA to which arrhythmic mutations were mapped are important to enhance expression.

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2002-09-01
2020-01-23
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