Department of Structural and Functional Biology, University of Naples Federico II, Via Cinthia 4, 80126 Naples, Italy.
J Bacteriol. 2011 Dec;193(23):6664-73. doi: 10.1128/JB.06121-11. Epub 2011 Oct 7.
The cotG and cotH genes of Bacillus subtilis encode two previously characterized spore coat proteins. The two genes are adjacent on the chromosome and divergently transcribed by σ(K), a sporulation-specific σ factor of the RNA polymerase. We report evidence that the cotH promoter maps 812 bp upstream of the beginning of its coding region and that the divergent cotG gene is entirely contained between the promoter and the coding part of cotH. A bioinformatic analysis of all entirely sequenced prokaryotic genomes showed that such chromosomal organization is not common in spore-forming bacilli. Indeed, CotG is present only in B. subtilis, B. amyloliquefaciens, and B. atrophaeus and in two Geobacillus strains. When present, cotG always encodes a modular protein composed of tandem repeats and is always close to but divergently transcribed with respect to cotH. Bioinformatic and phylogenic data suggest that such genomic organizations have a common evolutionary origin and that the modular structure of the extant cotG genes is the outcome of multiple rounds of gene elongation events of an ancestral minigene.
枯草芽孢杆菌 cotG 和 cotH 基因编码两种先前已鉴定的孢子外壳蛋白。这两个基因在染色体上相邻，由 σ(K)转录，σ(K)是 RNA 聚合酶的一种特定于孢子形成的 σ 因子。我们报告了证据表明 cotH 启动子位于其编码区起点上游 812bp 处，并且与之 divergently 转录的 cotG 基因完全包含在 cotH 的启动子和编码部分之间。对所有完全测序的原核基因组的生物信息学分析表明，这种染色体组织在产芽孢杆菌中并不常见。事实上，CotG 仅存在于枯草芽孢杆菌、解淀粉芽孢杆菌和萎缩芽孢杆菌以及两个地芽孢杆菌菌株中。当存在时，cotG 总是编码一种由串联重复组成的模块化蛋白质，并且总是靠近但 divergently 转录与 cotH。生物信息学和系统发育数据表明，这种基因组组织具有共同的进化起源，并且现存的 cotG 基因的模块化结构是祖先 minigene 的多次基因延长事件的结果。
