Negative Regulation by Lambda: Repression of Lambda RNA Synthesis in Vitro and Host Enzyme Synthesis in Vivo

Abstract

REPRESSION BY THE cI PROTEIN OF IN VITRO RNA SYNTHESIS
The role of the cI gene in repression of viral functions has been extensively investigated. Experiments on phage production (Kaiser and Jacob, 1957; Thomas, 1966; Pereira da Silva and Jacob, 1967; Ptashne and Hopkins, 1968) and in vivo transcription (Isaacs et al., 1965) have suggested that the cI protein (or λ repressor) acts on sites within a small region of the λ genome (the imm region, see Fig. 1) to repress transcription of the adjacent “early” genes to the left and right of the cI gene. In vitro experiments have supported this model by the demonstration that the cI protein binds to the imm (immunity) region of λ DNA (Ptashne, 1967), probably at sites just to the left and right of the cI gene (Ptashne and Hopkins, 1968). Based on these results the cI protein should inhibit in vitro RNA synthesis from a λ DNA template, and this inhibition should be specific to the early region. Previous experiments (Echols et al., 1968) have shown an inhibition of RNA synthesis in a relatively crude in vitro system. In this paper, we report studies of a more highly purified cI protein, using a more refined analysis of the RNA synthesis reaction. The results show that the cI protein can strongly inhibit RNA synthesis from early λ genes and probably acts without any cofactors. A similar conclusion has been derived by Chadwick et al. (1970) and Steinberg and Ptashne (in preparation).

Purification of...