TRANSCRIPTION OF THE HALOPHAGE PHI-H REPRESSOR GENE IS ABOLISHED BY TRANSCRIPTION FROM AN INVERSELY ORIENTED LYTIC PROMOTER

The temperate phage Phi PH of the extremely halophilic archaebacterium Halobacterium salinarium encodes a repressor, Rep, which in the immun e state represses the production of an early lytic transcript, denoted T4. Rep acts at the transcriptional level by blocking the promoter fo r T4. The promoter for the rep gene itself is positioned back to back to the promoter for T4, in a manner analogous to that of the cI/cro ge nes in bacteriophage lambda. Transcription of the rep gene does not oc cur when the phage is growing lytically. We show that this represson o f rep transcription during lytic growth is due to the transcription pe r se from the stronger, oppositely oriented promoter for T4, without t he need of a phage gene product.