Promoter for the establishment of repressor synthesis in bacteriophage lambda.

Transcription of the lambda repressor gene (cI) is positively regulated by the phage-encoded proteins cII and cIII. We have isolated and characterized the 5'-terminal region of this RNA and shown that it originates at a promoter (pE) located between genes cro and cII. The DNA sequence of this promoter shows little homology to other known promoters. Initiation of transcription from PE is abolished by the cis-dominant mutations cY; these mutations alter the "-10" and "-35" regions of the promoter. We propose that the "-35" region is the site of activation of PE, possibly via the direct interaction of protein cII.