TRANSCRIPTION ACTIVATION OR REPRESSION BY PHAGE PHI-29 PROTEIN P4 DEPENDS ON THE STRENGTH OF THE RNA POLYMERASE-PROMOTER INTERACTIONS

Phage Phi 29 protein p4 activates the late A3 promoter and represses t he early A2c promoter, in both cases by binding upstream from RNA poly merase (RNAP) and interacting with the C-terminal domain of the RNAP a lpha subunit. To investigate how this interaction leads to activation at PA3 and to repression at PA2c, mutant promoters were constructed. W e show that the position of protein p4 relative to that of RNAP, which is different al each promoter, does not dictate the outcome of the in teraction. Rather, in the absence of a -35 consensus box for sigma(A)- RNAP activation was observed, while in its presence repression occurre d. The results support the view that stabilization of RNAP at the prom oter over a threshold level leads to repression.