Lytic Mode of Lambda Development

Abstract

Lytic growth of bacteriophage requires the concerted expression of a number of functions, products of both viral and host genes. These functions promote transcription, replication, DNA processing, and packaging. Additionally, temperate phage such as λ, which can grow either lytically or lysogenically, must insure that once the decision to adopt one of the alternative modes of existence has been made, functions that can interfere with that mode are not expressed. In the lytic mode, the phage functions must be sequentially expressed, i.e., replication must precede packaging which, in turn, must precede lysis. Thus, although phage propagation occurs in a relatively short time—some 45 minutes for λ—it follows a strictly coordinated developmental plan.

In this paper we review current knowledge of λ lytic development. The lysogenic program is discussed by Wulff and Rosenberg and by Echols and Guarneros (both this volume). Our discussion focuses on (1) gene organization, (2) patterns of mRNA synthesis, and (3) regulatory controls of gene expression. The role of the λN function in regulating the lytic cycle is stressed. This is, in part, because N function is among the best characterized regulatory proteins and, also, its action typifies a mechanism of regulation based upon transcription termination-antitermination. For further background material and discussions from different perspectives, see Echols (1971), Weisberg et al. (1977), and Herskowitz and Hagen (1980).

GENETIC ORGANIZATION
The λ genome expresses approximately 50 proteins (Szybalski and Szybalski 1979). In this section we discuss the arrangement of the λ genes with respect to the...