FUNCTIONAL ROLES FOR THE GLUTAMINES WITHIN THE GLUTAMINE-RICH REGION OF THE TRANSCRIPTION FACTOR-SIGMA-54

Single and multiple point mutations were introduced to change the 12 g lutamine residues within a 37-amino acid region of sigma54. Multiple c hanges are shown to be required in order to interfere significantly wi th the function of this protein which is associated with enhancer-depe ndent bacterial transcription. Mutation of the central 4 glutamines le ads to the production of less m-RNA, caused by an inability to fully o pen the promoter start site. DNA binding, however, is normal. Mutation of 4 other adjacent glutamines causes the promoter start site to open more readily than wild type, although this enhanced opening is not ac companied by more mRNA. The emhanced DNA melting is not caused by enha nced promoter binding, as indicated by normal protection of the polyme rase-bound promoter against dimethyl sulfate attack. The results sugge st that multiple glutamines play a role in transducing the melting sig nal from the enhancer protein to the polymerase.