Dastur Anahita, Kumar Pradeep, Ramesh Sneha, Vasanthakrishna Mundodi, Varshney Umesh
Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, 560 012, India.
Arch Microbiol. 2002 Oct;178(4):288-96. doi: 10.1007/s00203-002-0460-0. Epub 2002 Jul 24.
Initiation of protein synthesis is a major post-transcriptional regulatory step in gene expression. The initiator tRNA gene from Mycobacterium smegmatis, a fast-growing mycobacterium, was characterized and compared with its counterpart from Mycobacterium tuberculosis, a slow-growing mycobacterium. In both mycobacteria, the functional initiator tRNA genes were found in a single copy. Unlike the M. tuberculosis initiator tRNA, the CCA end of the M. smegmatis initiator is not encoded in the gene, and it is most likely added post-transcriptionally. Transcription start site mapping allowed accurate assignment of the hexameric -10 and -35 promoter elements for both genes. These elements of the M. smegmatis initiator tRNA gene contain single nucleotide changes compared to their respective counterparts in the M. tuberculosis gene. Chloramphenicol acetyl transferase reporter assays suggested that the promoter of the initiator tRNA gene from M. smegmatis is twice as strong as that of M. tuberculosis, irrespective of whether the assays were performed in the fast-growing homologous host (M. smegmatis) or the slow-growing heterologous host (M. tuberculosis). Characterization of the M. smegmatis metU promoter, in this study, provides a valuable tool for the expression of genes in mycobacteria.
蛋白质合成的起始是基因表达中一个主要的转录后调控步骤。对快速生长的耻垢分枝杆菌的起始tRNA基因进行了表征，并与缓慢生长的结核分枝杆菌的对应基因进行了比较。在这两种分枝杆菌中，功能性起始tRNA基因均以单拷贝形式存在。与结核分枝杆菌起始tRNA不同，耻垢分枝杆菌起始tRNA的CCA末端不是由基因编码的，很可能是转录后添加的。转录起始位点定位使得能够准确确定这两个基因的六聚体-10和-35启动子元件。与结核分枝杆菌基因中的相应元件相比，耻垢分枝杆菌起始tRNA基因的这些元件存在单核苷酸变化。氯霉素乙酰转移酶报告基因检测表明，无论检测是在快速生长的同源宿主（耻垢分枝杆菌）还是缓慢生长的异源宿主（结核分枝杆菌）中进行，耻垢分枝杆菌起始tRNA基因的启动子强度都是结核分枝杆菌的两倍。本研究中对耻垢分枝杆菌metU启动子的表征为分枝杆菌中基因的表达提供了一个有价值的工具。
