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。     

Protein-DNA cross-linking at the lac promoter.

We report the results of photo-cross-linking of RNA polymerase and the cyclic AMP receptor protein (CRP) to the lac UV5 promoter region carried on either a linear fragment or a supercoiled plasmid. We have devised a protocol that allows the localisation of bases in contact with the protein. RNA polymerase makes contacts within the -10 and -35 regions of the promoter, essentially on the non-template strand. The CRP contact points found in a binary complex are affected by the formation of the ternary complex containing RNA polymerase. Supercoiling has no effect on the position of contacts in any of the complexes. These conclusions were derived from experiments performed using a generally applicable, non-interfering technique that reveals direct contacts between proteins and nucleic acids in nucleoprotein complexes.