CONVERTING ESCHERICHIA-COLI RNA-POLYMERASE INTO AN ENHANCER-RESPONSIVE ENZYME - ROLE OF AN NH2-TERMINAL LEUCINE PATCH IN SIGMA(54)

The protein sigma(54) associates with Escherichia coli core RNA polyme rase to form a holoenzyme that binds promoters but is inactive in the absence of enhancer activation, Here, mutants of sigma(54) enabled pol ymerases to transcribe without enhancer protein and adenosine triphosp hate. The mutations are in leucines within the NH2-terminal glutamine- rich domain of sigma(54). Multiple leucine substitutions mimicked the effect of enhancer protein, which suggests that the enhancer protein f unctions to disrupt a leucine patch. The results indicate that sigma(5 4) acts both as an inhibitor of polymerase activity and as a receptor that interacts with enhancer protein to overcome this inhibition, and that these two activities jointly confer enhancer responsiveness.