Bayer M G, Heinrichs J H, Cheung A L
Laboratory of Bacterial Pathogenesis and Immunology, The Rockefeller University, New York, 10021, USA.
J Bacteriol. 1996 Aug;178(15):4563-70. doi: 10.1128/jb.178.15.4563-4570.1996.
The global regulator sar in Staphylococcus aureus controls the synthesis of a variety of cell wall and extracellular proteins, many of which are putative virulence factors. The sar locus in strain RN6390 contains a 339-bp open reading frame (sarA) and an 860-bp upstream region. Transcriptional analyses of this locus revealed three different transcripts of 0.58, 0.84, and 1.15 kb (designated sarA, sarC, and sarB, respectively). All three transcripts seemed to be under temporal, growth cycle-dependent regulation, with sarA and sarB being most abundant in early log phase and the sarC concentration being highest toward the late stationary phase. Mapping of the 5' ends of the sar transcripts by primer extension and modified S1 nuclease protection assays demonstrated that transcription is initiated from three separate, widely spaced promoters. The 3' ends of all three sar transcripts are identical, and transcriptional termination occurs upstream of a typical prokaryotic poly(T) termination signal. Northern (RNA) analysis of sar mutant clones containing plasmids that comprised various promoters and the termination signal revealed that individual transcripts can be generated from each of the three promoters, thus suggesting possible activation as independent promoters. The multipromoter system, from which transcription is initiated, bears conserved features for recognition by homologous sigma 70 transcription factors and also by those expressed in the general stress response. Downstream of the two distal promoters (P3 and P2) are two regions potentially encoding short peptides. It is conceivable that posttranslational cooperation between these short peptides and the sarA gene product occurs to modulate sar-related functions. Complementation studies of a sar mutant with a clone expressing all three sar transcripts showed that this clone was able to restore the sar wild-type phenotype to the sar mutant.
金黄色葡萄球菌中的全局调控因子sar控制着多种细胞壁和细胞外蛋白的合成，其中许多是假定的毒力因子。RN6390菌株中的sar基因座包含一个339 bp的开放阅读框（sarA）和一个860 bp的上游区域。对该基因座的转录分析揭示了三种不同的转录本，大小分别为0.58、0.84和1.15 kb（分别命名为sarA、sarC和sarB）。所有这三种转录本似乎都受到时间、生长周期依赖性调控，sarA和sarB在对数早期最为丰富，而sarC的浓度在稳定期末期最高。通过引物延伸和改良的S1核酸酶保护试验对sar转录本的5'端进行定位，结果表明转录起始于三个单独的、间隔较远的启动子。所有三种sar转录本的3'端相同，转录终止发生在典型的原核poly(T)终止信号上游。对含有各种启动子和终止信号的质粒的sar突变克隆进行Northern（RNA）分析，结果表明三种启动子中的每一种都可以产生单独的转录本，因此表明可能作为独立的启动子被激活。转录起始的多启动子系统具有保守特征，可被同源的sigma 70转录因子以及一般应激反应中表达的转录因子识别。在两个远端启动子（P3和P2）的下游是两个可能编码短肽的区域。可以想象，这些短肽与sarA基因产物之间的翻译后协同作用会调节与sar相关的功能。用表达所有三种sar转录本的克隆对sar突变体进行互补研究，结果表明该克隆能够将sar野生型表型恢复到sar突变体。
