Mutations in KaiA, a clock protein, extend the period of circadian rhythm in the cyanobacterium Synechococcus elongatus PCC 7942.
KaiA KaiB and KaiC are essential circadian clock proteins in the unicellular cyanobacterium Synechococcus elongatus PCC 7942. KaiA protein activates transcription of the kaiBC operon, which is believed to be a crucial step in the oscillating feedback loop of cyanobacteria. In this study, approximately approximately 400 mutations were introduced into kaiA 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 kaiBC expression. However, several mutations resulted in low-amplitude oscillations or arrhythmia, which were accompanied by lowered kaiBC 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 kaiBC 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 kaiBC expression.
Nishimura
Hideya
H
First Department of Internal Medicine, Nagoya University, School of Medicine Tsurumai 65, Showa, Nagoya 466-8550, Japan2.|Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa, Nagoya 464-8602, Japan1.
Nakahira
Yoichi
Y
Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa, Nagoya 464-8602, Japan1.
Imai
Keiko
K
Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa, Nagoya 464-8602, Japan1.
Tsuruhara
Akiko
A
Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa, Nagoya 464-8602, Japan1.
Kondo
Hisayo
H
Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa, Nagoya 464-8602, Japan1.
Hayashi
Hiroshi
H
First Department of Internal Medicine, Nagoya University, School of Medicine Tsurumai 65, Showa, Nagoya 466-8550, Japan2.
Hirai
Makoto
M
First Department of Internal Medicine, Nagoya University, School of Medicine Tsurumai 65, Showa, Nagoya 466-8550, Japan2.
Saito
Hidehiko
H
First Department of Internal Medicine, Nagoya University, School of Medicine Tsurumai 65, Showa, Nagoya 466-8550, Japan2.
Kondo
Takao
T
Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Corporation (JST), Furo-cho, Chikusa, Nagoya 464-8602, Japan1.
D001683:Biological Clocks / Q000235:genetics / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D000458:Cyanobacteria / Q000235:genetics / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D017930:Genes, Reporter; D008163:Luminescent Measurements; D008954:Models, Biological; D005810:Multigene Family; D016296:Mutagenesis; D009154:Mutation; D009876:Operon