ROLE OF OPERATOR SUBSITES IN ARE REPRESSION

By binding to adjacent subsites in its 21 base-pair operator, Are repr esses transcription from two divergent promoters, P-ant and P-mnt, in the immunity I operon of bacteriophage P22. Are dimers bind to each su bsite with nanomolar affinities and interact through protein-protein i nteractions to stabilize binding further. Here, we show that an Are di mer bound to a single subsite reduces the rate of RNA polymerase open- complex formation and represses transcription from P-ant and P-mnt pro moter variants to varying degrees. Occupancy of the subsite proximal t o the P-ant-35 region results in significantly greater repression than occupancy of the -10 proximal subsite. For repression of P-mnt, Are b ound at the -10 proximal subsite is more effective than Are bound at t he -35 proximal subsite. Because of the divergent orientations of the two promoters, the -35 proximal site in P-ant is the same as the -10 p roximal site in P-mnt. Thus, in both cases, the same operator subsite is primarily responsible for repression of transcription initiation. ( C) 1996 Academic Press Limited