transcription in prokaryotes

RNA polymerase…

does not need primer to start synthesis

holoenzyme

sigma factor

sigma factor plays a regulatory function in the

initiation of RNA transcription

template binding via the promoter

leads to unwinding of the DNA, making template accessible

core promoters in bacteria consist of 2 conserved sequences

-10 and 35 (-10 region called Pribnow Box)

cis-regulatory elements

promoters and other DNA regulatory sequences controlling gene expression

trans-regulatory elements

non-DNA molecules that bind to cis-elements to influence gene expression

mutations in promoter sequences may

severely reduce the initiation of gene expression

Initiation: after a few ribonucleotides have been added to the growing RNA chain…

the sigma factor dissociates from the holoenzyme and the core enzyme continues elongation

Chain elongation:

core enzyme continues elongating the RNA chain until hits termination sequence

termination

termination sequence cause transcript to form hairpin loop

termination sequences are often

GC-rich inverted repeats

intrinsic termination

hairpin structure cause RNA pol to stall and causes transcriptional factors to dissociate

Rho-dependent termination

Rho protein binds to a sequence and chases the RNA pol in the 3’ direction

when RNA pol reaches the hairpin structure, it pauses and

breaks H-bonds between RNA and DNA causing transcriptional termination

Rho moves through hairpin and causes dissociation of RNA pol by

unwinding the RNA-DNA hybrid