Mutations in KaiA, a clock protein, extend the period of circadian rhythm in the cyanobacterium Synechococcus elongatus PCC 7942
Mutations in KaiA, a clock protein, extend the period of circadian rhythm in the cyanobacterium Synechococcus elongatus PCC 7942
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DOI：
10.1099/00221287-148-9-2903
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发表时间：
2002-09-01
期刊：
影响因子：
2.8
通讯作者：
Kondo, T
中科院分区：
文献类型：
--
作者：
Nishimura, H;Nakahira, Y;Kondo, T
Kaia Kaib和KaiC是单细胞蓝藻细长聚球藻PCC7942中必需的昼夜节律时钟蛋白。KaIA蛋白激活了kaiBC操纵子的转录，这被认为是蓝藻振荡反馈环中的关键步骤。在这项研究中，通过基于PCR的突变将类似的400个突变引入KaIA，并用生物发光报告对这些突变的节律表型进行了研究。与Kaib或KaiC突变相比，绝大多数KaiA突变延长了这一周期，但很少会缩短。在不降低kaiBC表达平均值或峰值的情况下，该周期可延长至35h。然而，一些突变导致低幅度振荡或心律失常，并伴随着kaiBC转录降低。这些结果表明，KaIA蛋白可以直接(通过未知的生化机制)或间接(通过降低kaiBC的表达)改变昼夜节律的周期长度。在34个突变体中发现了KaiA的特异性突变。虽然突变被映射到KaIA序列的不同位置，但发现了两组改变周期的突变。这表明这些区域是KaIA蛋白中决定周期长度的重要结构域。另一方面，心律失常突变所映射到的KaIA内的不同序列对于增强KaiBC的表达是重要的。
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, similar to400 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.