A POSITIVE CONTROL MUTANT OF THE TRANSCRIPTION ACTIVATOR PROTEIN FIS

The FIS protein is a transcription activator of rRNA and other genes i n Escherichia coli. We have identified mutants of the FIS protein resu lting in reduced rrnB P1 transcription activation that nevertheless re tain the ability to bind DNA in vivo. The mutations map to amino acid 74, the N-terminal amino acid of the protein's helix-turn-helix DNA bi nding motif, and to amino acids 71 and 72 in the adjoining surface-exp osed loop. In vitro analyses of one of the activation-defective mutant s (with a G-to-S mutation at position 72) indicates that it binds to a nd bends rrnB P1 FIS site I DNA the same as wild-type FIS. These data suggest that amino acids in this region of FIS are required for transc ription activation by contacting RNA polymerase directly, independent of any other role(s) this region may play in DNA binding or protein-in duced bending.