Progress Since 1970

Abstract

This paper reviews progress in λ biology since the predecessor to this book, The Bacteriophage Lambda, was written in 1970. References are given to other papers in the volume, and these should be consulted for detailed discussions and access to the primary literature.

LYSIS/LYSOGENY DECISION
In the past decade gratifying progress has been made in our understanding of the regulatory circuits of the phage, particularly those dealing with the “decision” between lytic growth and lysogeny (Friedman and Gottesman; Wulff and Rosenberg; Echols and Guarneros; Gussin et al.). Stripped to its essentials, the decision can be understood as a competition between the products of genes cI and cro for occupancy of the operator o_R. These two proteins, both of which are transcriptional repressors, compete for the operator and repress each other’s synthesis. The most important modulator of this balance is the cII protein, which is itself regulated by both cI and cro, as well as by cIII and the host gene hflA.

Studies on the structures of operators have elucidated how the cI and cro proteins act. o_R (and o_L) contains three adjacent binding domains, and the rules for how cI and cro proteins bind to them (order of binding, cooperativity, affinity) are different for the two repressor proteins in ways that can be understood as contributing to the observed behavior of the regulatory circuits. The recent determinations by X-ray diffraction of the structures of cro protein and the DNA-binding portion of cI protein reveal detailed structural information about the protein-DNA...