Establishment of Repressor Synthesis

Abstract

INTRODUCTION
mRNA encoding the cI repressor of bacteriophage λ can be initiated at either of two promoters, which function at different stages in the λ life cycle. In the lysogenic state, repressor transcription initiates from the p_RM promoter, which lies immediately adjacent to the cI gene (Fig. 1). This promoter is positively regulated by the cI-gene product and both structurally and functionally overlaps with the promoter-operator signals (p_Ro_R) controlling the major rightward operon of λ. In contrast, when λ infects a sensitive cell, repressor transcription originates from the p_RE promoter, which lies several hundred base pairs upstream of the cI gene in the λy region (Fig. 1). This promoter structurally overlaps the region encoding the aminoterminal amino acid sequence of the cII gene. Transcription from p_RE is also positively regulated and, in this case, the activator is the cII protein. The cII protein also activates transcription from p_I, the promoter for the λ integrase gene. Thus, the cII protein coordinately regulates the two transcription units required for the lysogenic response and thereby acts as a major determinant in controlling the balance between lytic and lysogenic development. The cII activity is itself regulated at multiple levels (transcription, translation, processing, stability, and so on), and a variety of phage and host-encoded functions take part in this regulation.

In this paper we examine the p_RE transcription unit, with particular emphasis on the p_RE promoter signal and its mode of activation by cII protein. We examine the cII protein both genetically and biochemically and...