Transcriptional regulation of early functions of bacteriophage φ80

Abstract

To study the expression of early functions of φ80 phage, various segments from the early region were transcribed with RNA polymerase. Two major transcripts (from promoters P L and P R) whose synthesis was inhibited by the CI protein were identified. Synthesis of the third major transcript (from promoter P RM) was induced by the CI protein. These studies define two operator-promoter regions, O LP L and O RP RP RM. This mode of transcription from the early region is similar to that of phage λ. However, there are the following major differences. One is the presence of a ρ-independent terminator of transcription from promoter P L located immediately after gene N and the absence of a ρ-dependent terminator that corresponds to t R1 of λ The other is the uniqueness of the structure and function of the operators. Both O L and O R 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 λ proteins to the λ operators. For example, binding of the φ80 CI protein to the O R1 site is less tight than its binding to the O R2 or O R3 site. The gene 30 protein binds to the O R1 site as tightly as to the O R3 site.