DNA binding regions of Q proteins of phages lambda and phi80.

Bacteriophage lambda gene Q protein and the related proteins of other lambdoid phages are transcription antiterminators that interact both with DNA in the late gene promoter segment and with RNA polymerase subunits. Using hybrids between Q of lambda and the related Q of phage 80, we characterized elements of both Q and DNA that contribute to the DNA binding function. In particular, we found a C-terminal segment of the protein that is responsible for binding specificity and an approximately 15 residue segment on a predicted alpha helix within this segment at which alanine substitutions decrease DNA binding. We identified a six-nucleotide segment located between the -35 and -10 promoter elements that confers binding specificity and is the site of point mutants that impair binding, and we isolated suppressors in lambda Q that restore binding function by increasing the overall binding affinity. We also identified putative zinc finger structures in both proteins.