DNA strand specificity in promoter recognition by RNA polymerase.

DNA strand and enzyme subunit specificities involved in the interaction between E. coli RNA polymerase and T7 DNA were studied by photo-crosslinking techniques. In non-specific enzyme-DNA complexes, subunits, sigma, beta, and beta' were crosslinked to both strands of the DNA. Under conditions leading to specific enzyme-promoter complexes, however, only sigma and beta subunits were crosslinked. The sigma subunit was crosslinked preferentially to the non-sense strand at promoter sites. No such strand specificity was observed for the beta subunit. These results provide insight into the molecular mechanism of promoter recognition and indicate that the interaction between RNA polymerase and DNA template is different at promoters and at non-specific sites.     

细菌转录起始调控机制*

原核生物同一种群的每个细胞都是和外界环境直接接触的,它们主要通过开启或关闭某些基因的表达来适应环境条件。所以,环境因子往往是调控的效应因子,必须严格调控转录来确保细胞对环境改变做出有效且充分的反应。原核生物基因的表达受多种因素的调控,而对于大多数细菌来说,调控基因表达的关键步骤是启动子识别和RNA聚合酶启动转录。在细菌的细胞中,可以通过调节RNA聚合酶的活性以及改变RNA聚合酶对启动子的结合来优化基因的转录过程以适应不同环境变化。总结了目前已发现的参与细菌细胞转录调节的各类因子,从这些因子对启动子的作用、RNA聚合酶的作用以及两者的相互作用等方面阐述它们调控基因表达的分子机制。总结多种基因调控的作用,加深对转录起始过程的认识,希望能对未来调控转录起始过程来实现目标基因的高效表达和不利基因的抑制表达提供思路,为以后的工业菌株改造提供依据。     

Substitution of RNA-polymerase sigma-subunits and transcription regulation

Recent data on regulation of gene activity in bacteria by substitution of RNA polymerase sigma subunits are reviewed. The htpR gene which controls the switch-on of the Escherichia coli heat-shock protein synthesis codes for sigma 32 subunit. sigma 32-containing RNA polymerase transcribes the heat-shock genes in vitro from specific promoters of no use for RNA polymerase containing the major sigma 70 subunit. Several minor sigma subunits have been found in Bacillus subtilis vegetative cells, in addition to the major sigma 55 subunit, differing in the specificity of promoter recognition. Many B. subtilis genes are controlled by tandemly located promoters recognized by RNA polymerases carrying different sigma subunits. sigma 29 subunit is encoded by spoIIG gene and is probably involved in the regulation of sporulation. Specific sigma subunits for transcribing "middle" or "late" genes are encoded by a number of phages.