IDENTIFICATION OF A DNA-CONTACTING SURFACE IN THE TRANSCRIPTION FACTOR SIGMA-54

The transcription factor sigma-54 (sigma 54) is a sequence-specific DN A-binding protein that directs RNA polymerase to a particular class of promoter. The interaction of sigma 54 with promoter DNA has been anal ysed by protein-DNA crosslinking and enzymatic and chemical proteolysi s. Direct physical evidence for a DNA-contacting surface within the ca rboxy-terminal one-third of the protein has been obtained. This region of sigma 54 is likely to be close to the surface of the protein, and contacts DNA when either sigma 54 or the sigma 54-holoenzyme bind spec ifically to promoter DNA. The amino-terminal region of sigma 54 appear s to be highly susceptible to proteolysis, and its integrity influence s the accessibility towards proteolysis of a second region of sigma 54 , which includes the DNA-contacting surface. Thus the amino-terminal r egion of sigma 54 may have a role in influencing its DNA-binding prope rties, the major determinants of which appear to reside in the carboxy -terminal one-third of the protein.