Transcription of the halophage phi H repressor gene is abolished by transcription from an inversely oriented lytic promoter.

The temperate phage phi H of the extremely halophilic archaebacterium Halobacterium salinarium encodes a repressor, Rep, which in the immune state represses the production of an early lytic transcript, denoted T4. Rep acts at the transcriptional level by blocking the promoter for 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 genes in bacteriophage lambda. Transcription of the rep gene does not occur when the phase is growing lytically. We show that this repressor of rep transcription during lytic growth is due to the transcription per se from the stronger, oppositely oriented promoter for T4, without the need of a phage gene product.