O

C) Presence of anti-termination factor

Promoter

Recognition Termination eite eite

Anti-termination factor

Anti-termination factor beyond the terminator (Fig. 9.26). This mechanism for controlling gene expression is common in bacteriophages but is also found for a few bacterial genes.

Anti-termination factors attach themselves to the RNA polymerase before it reaches the terminator. The recognition sequences for anti-termination are found in the DNA well upstream of the terminator. As the RNA polymerase passes by, the anti-termination factors are loaded on. They remain attached and allow the RNA polymerase to travel past the stem and loop region of the terminator without pausing. Consequently, termination is suppressed (Fig. 9.26).

Anti-termination in E. coli involves several Nus proteins. NusA protein is probably attached to the core RNA polymerase shortly after the sigma factor is lost just after initiation. NusA itself actually promotes termination, apparently by increasing the duration of pauses at hairpin structures. NusA and sigma cannot both bind to the core enzyme simultaneously. As long as RNA polymerase is attached to DNA, the Nus proteins cannot be dislodged. However, addition of sigma displaces NusA from free RNA

Nus proteins A family of bacterial proteins involved in termination of transcription and/or in anti-termination NusA protein A bacterial protein involved in termination of transcription

Terminator _

DNA Promoter Gene to lté transcribed

Was this article helpful?

0 0

Post a comment