Practice question

In bacteria, sigma factor combines with core RNA polymerase to form holoenzyme that recognizes -10 and -35 promoter motifs and unwinds DNA. During early elongation, the sigma 3.2 linker remains lodged inside the RNA exit channel, obstructing growth beyond a few nucleotides. Once transcript reaches 9 to 11 nucleotides, steric clash ejects region 3.2, disrupts sigma-DNA and sigma-core contacts, and triggers conformational change to processive elongation complex. Sigma is released after promoter escape, recycles to new core enzymes, while NusA, NusG and other regulators bind elongating polymerase.