Katayama Mitsunori, Kondo Takao, Xiong Jin, Golden Susan S
Department of Biology, Texas A&M University, College Station, Texas 77843-3258, USA.
J Bacteriol. 2003 Feb;185(4):1415-22. doi: 10.1128/JB.185.4.1415-1422.2003.
We generated random transposon insertion mutants to identify genes involved in light input pathways to the circadian clock of the cyanobacterium Synechococcus elongatus PCC 7942. Two mutants, AMC408-M1 and AMC408-M2, were isolated that responded to a 5-h dark pulse differently from the wild-type strain. The two mutants carried independent transposon insertions in an open reading frame here named ldpA (for light-dependent period). Although the mutants were isolated by a phase shift screening protocol, the actual defect is a conditional alteration in the circadian period. The mutants retain the wild-type ability to phase shift the circadian gene expression (bioluminescent reporter) rhythm if the timing of administration of the dark pulse is corrected for a 1-h shortening of the circadian period in the mutant. Further analysis indicated that the conditional short-period mutant phenotype results from insensitivity to light gradients that normally modulate the circadian period in S. elongatus, lengthening the period at low light intensities. The ldpA gene encodes a polypeptide that predicts a 7Fe-8S cluster-binding motif expected to be involved in redox reactions. We suggest that the LdpA protein modulates the circadian clock as an indirect function of light intensity by sensing changes in cellular physiology.
我们生成了随机转座子插入突变体，以鉴定参与蓝藻聚球藻PCC 7942生物钟光输入途径的基因。分离出了两个突变体AMC408-M1和AMC408-M2，它们对5小时暗脉冲的反应与野生型菌株不同。这两个突变体在一个开放阅读框中携带独立的转座子插入，该开放阅读框在此命名为ldpA（光依赖周期）。尽管这些突变体是通过相移筛选方案分离出来的，但实际缺陷是生物钟周期的条件性改变。如果针对突变体生物钟周期缩短1小时的情况校正暗脉冲的给药时间，这些突变体保留了使生物钟基因表达（生物发光报告基因）节律发生相移的野生型能力。进一步分析表明，这种条件性短周期突变体表型是由于对通常调节聚球藻生物钟周期的光梯度不敏感导致的，在低光强度下会延长周期。ldpA基因编码一种多肽，该多肽预测有一个预期参与氧化还原反应的7Fe-8S簇结合基序。我们认为，LdpA蛋白通过感知细胞生理变化，作为光强度的间接函数来调节生物钟。
