Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 148

When RNA polymerase holoenzyme first binds to the promoter, the DNA is double stranded. The resulting complex is called the RP_c, because the DNA strands are still “closed.” In the next step, the β′ pincer of the crab claw closes around the DNA to form the active-site channel around the template strand of the DNA. This allows the σ₂ region to separate the strands of DNA at the –10 region and bind to the nontemplate strand in a process called isomerization (Figures 2.8 and 2.9). Recall that AT base pairs are less stable than GC pairs, so the AT-rich –10 sequence is relatively easy to melt. The complex is now called the open complex (RP_o), since the strands of DNA at the –10 region of the promoter are “open.” The +1 nucleotide of the template strand is held in the active-site channel, where the polymerization reaction is about to occur.