Xu Y, Mori T, Johnson C H
Department of Biology, Box 1812-B, Vanderbilt University, Nashville, TN 37235, USA.
EMBO J. 2000 Jul 3;19(13):3349-57. doi: 10.1093/emboj/19.13.3349.
The cyanobacterial gene cluster kaiABC encodes three essential circadian clock proteins: KaiA, KaiB and KaiC. The KaiB and KaiC protein levels are robustly rhythmical, whereas the KaiA protein abundance undergoes little if any circadian oscillation in constant light. The level of the KaiC protein is crucial for correct functioning of the clock because induction of the protein at phases when the protein level is normally low elicits phase resetting. Titration of the effects of the inducer upon phase resetting versus KaiC level shows a direct correlation between induction of the KaiC protein within the physiological range and significant phase shifting. The protein synthesis inhibitor chloramphenicol prevents the induction of KaiC and blocks phase shifting. When the metabolism is repressed by either translational inhibition or constant darkness, the rhythm of KaiC abundance persists; therefore, clock protein expression has a preferred status under a variety of conditions. These data indicate that rhythmic expression of KaiC appears to be a crucial component of clock precession in cyanobacteria.
蓝藻基因簇kaiABC编码三种基本的生物钟蛋白：KaiA、KaiB和KaiC。KaiB和KaiC的蛋白水平呈现强烈的节律性，而在持续光照下，KaiA的蛋白丰度几乎没有昼夜振荡（即便有也很微小）。KaiC蛋白的水平对于生物钟的正常运行至关重要，因为在该蛋白水平通常较低的阶段诱导其表达会引发相位重置。滴定诱导剂对相位重置与KaiC水平的影响表明，在生理范围内诱导KaiC蛋白与显著的相位偏移之间存在直接关联。蛋白质合成抑制剂氯霉素可阻止KaiC的诱导并阻断相位偏移。当通过翻译抑制或持续黑暗抑制代谢时，KaiC丰度的节律依然存在；因此，在各种条件下，生物钟蛋白的表达都具有优先地位。这些数据表明，KaiC的节律性表达似乎是蓝藻生物钟进动的关键组成部分。
