Promoter for the Establishment of Repressor Synthesis in Bacteriophage λ

Transcription of the λ 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 pEis 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.