Ito Hiroshi, Mutsuda Michinori, Murayama Yoriko, Tomita Jun, Hosokawa Norimune, Terauchi Kazuki, Sugita Chieko, Sugita Mamoru, Kondo Takao, Iwasaki Hideo
Division of Advanced Sciences, Ochadai Academic Production, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo, Tokyo, 112-8610, Japan.
Proc Natl Acad Sci U S A. 2009 Aug 18;106(33):14168-73. doi: 10.1073/pnas.0902587106. Epub 2009 Jul 30.
In the unicellular cyanobacterium Synechococcus elongatus PCC 7942, essentially all promoter activities are under the control of the circadian clock under continuous light (LL) conditions. Here, we used high-density oligonucleotide arrays to explore comprehensive profiles of genome-wide Synechococcus gene expression in wild-type, kaiABC-null, and kaiC-overexpressor strains under LL and continuous dark (DD) conditions. In the wild-type strains, >30% of transcripts oscillated significantly in a circadian fashion, peaking at subjective dawn and dusk. Such circadian control was severely attenuated in kaiABC-null strains. Although it has been proposed that KaiC globally represses gene expression, our analysis revealed that dawn-expressed genes were up-regulated by kaiC-overexpression so that the clock was arrested at subjective dawn. Transfer of cells to DD conditions from LL immediately suppressed expression of most of the genes, while the clock kept even time in the absence of transcriptional feedback. Thus, the Synechococcus genome seems to be primarily regulated by light/dark cycles and is dramatically modified by the protein-based circadian oscillator.
在单细胞蓝藻聚球藻属细长聚球藻PCC 7942中，基本上所有启动子活性在持续光照（LL）条件下都受生物钟调控。在此，我们使用高密度寡核苷酸阵列来探究野生型、缺失kaiABC基因的菌株以及过表达kaiC基因的菌株在LL和持续黑暗（DD）条件下全基因组范围的聚球藻基因表达的综合图谱。在野生型菌株中，超过30%的转录本以昼夜节律的方式显著振荡，在主观黎明和黄昏达到峰值。这种昼夜节律调控在缺失kaiABC基因的菌株中严重减弱。尽管有人提出KaiC在全局上抑制基因表达，但我们的分析表明，黎明表达的基因在过表达kaiC时上调，从而使生物钟在主观黎明时停滞。将细胞从LL条件转移到DD条件会立即抑制大多数基因的表达，而在没有转录反馈的情况下生物钟仍保持均匀的时间。因此，聚球藻基因组似乎主要受光/暗周期调控，并被基于蛋白质的生物钟振荡器显著改变。
