Although prokaryotic promoters vary considerably, two short regions
are shared in common by most promoters. Aregion on the nonsense
strand about 10 bp before transcription initiates (-10 sequence) has a consensus
5'-TATAAT-3' and another region about 35 bp up (-35 sequence)
has a consensus sequence 5'-TTGACA-3'. A consensus sequence contains
the nucleotide sequence most commonly encountered in a wide variety
|Figure 4-2 Roles of Sigma and Rho.
Most terminators at the end of a mRNA molecule code for a singlestranded
region that folds on itself due to hydrogen bonding between
complementary base pairs and codes for a final region containing many
uracils. The hairpin structure that forms interacts with the RNA polymerase
and stimulates its detachment from the DNA . Some terminators
require terminator proteins such as Rho (ρ) to be active (Figure
4-2d,e). These Rho-dependent terminators lack a poly-U region in the 3'
end of the terminator. The NusA protein is another termination factor that apparently binds directly to the RNApolymerase and catalyzes its release
when it comes to termination sites.