Inoue-Sakamoto Kaori, Gruber Tanja M, Christensen Suzanne K, Arima Hiromi, Sakamoto Toshio, Bryant Donald A
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, University Park, PA 16802, USA.
J Gen Appl Microbiol. 2007 Apr;53(2):89-104. doi: 10.2323/jgam.53.89.
Three genes, sigF, sigG and sigH, encoding group 3 sigma factors have been cloned and characterized in the marine cyanobacterium Synechococcus sp. strain PCC 7002. The sigF gene product was similar to sigma factors involved in general stress response and sporulation in other organisms, and the sigG and sigH gene products were similar to extracytoplasmic function (ECF) sigma factors. The sigG and sigH genes were associated with the putative regulatory genes and the sizes of transcripts for sigG and sigH genes were large enough to be cotranscribed with the associated downstream genes. The sigG downstream gene was designated sapG (sigG-associated protein), and yeast two-hybrid analysis demonstrated that SigG and SapG interact when produced in yeast cells. Null mutants of these three group 3 sigma factor genes were created by interposon mutagenesis. The growth of the sigF mutant strain was much slower than the wild-type strain at 15 degrees C, although the growth rates at 22 degrees C and 38 degrees C were identical to those of the wild-type strain. The sigG mutant could not grow continuously at 22 degrees C, and no growth occurred at 15 degrees C. Since SigG and SapG interact in yeast cells and the sigG and sapG mutants showed a similar growth phenotype, SapG is likely to be a regulatory protein for SigG involved in the same pathway in transcriptional regulation in this cyanobacterium.
编码第3组σ因子的三个基因sigF、sigG和sigH已在海洋蓝藻聚球藻属PCC 7002菌株中克隆并进行了表征。sigF基因产物与其他生物体中参与一般应激反应和孢子形成的σ因子相似，而sigG和sigH基因产物与胞外功能（ECF）σ因子相似。sigG和sigH基因与假定的调控基因相关，sigG和sigH基因转录本的大小足以与相关的下游基因一起转录。sigG下游基因被命名为sapG（sigG相关蛋白），酵母双杂交分析表明，SigG和SapG在酵母细胞中表达时会相互作用。通过插入诱变创建了这三个第3组σ因子基因的缺失突变体。sigF突变体菌株在15℃时的生长比野生型菌株慢得多，尽管在22℃和38℃时的生长速率与野生型菌株相同。sigG突变体在22℃时不能连续生长，在15℃时不生长。由于SigG和SapG在酵母细胞中相互作用，并且sigG和sapG突变体表现出相似的生长表型，因此SapG可能是参与该蓝藻转录调控同一途径的SigG的调控蛋白。
