Transcriptional regulation of early functions of bacteriophage phi 80

To study the expression of early functions of phi 80 phage, various segments from the early region were transcribed with RNA polymerase. Two major transcripts (from promoters PL and PR) whose synthesis was inhibited by the CI protein were identified. Synthesis of the third major transcript (from promoter PRM) was induced by the CI protein. These studies define two operator-promoter regions, OLPL and ORPRPRM. This mode of transcription from the early region is similar to that of phage lambda. However, there are the following major differences. One is the presence of a p-independent terminator of transcription from promoter PL located immediately after gene N and the absence of a p-dependent terminator that corresponds to tR1 of lambda. The other is the uniqueness of the structure and function of the operators. Both OL and OR operator regions consist of three sites, each containing a highly homologous 19 base-pair sequence. In each site, consensus octanucleotide sequences (half-sites) exhibit dyad symmetry, except in one of the sites where the sequences are arranged tandemly. In addition, each operator region also contains a single half-site. The modes of binding of the CI protein and gene 30 protein to these operator sites are quite different from those of the lambda proteins to the lambda operators. For example, binding of the phi 80 CI protein to the OR1 site is less tight than its binding to the OR2 or OR3 site. The gene 30 protein binds to the OR1 site as tightly as to the OR3 site.