Lambda DNA Replication

Abstract

INTRODUCTION
The replication of bacteriophage λ DNA depends on interactions with the bacterial host. As a repressed prophage, λ replicates passively, integrated into the host chromosome. As an active virus or as a plasmid, λ channels host enzymes to replicate its chromosome.

A single cycle of productive growth generates approximately 100 copies of the viral genome. During the latent period, distinct forms of λ DNA appear in an orderly progression (Fig. 1). The replication program can be divided into two phases: early and late. In the early phase, DNA synthesis initiates at a unique origin region on covalently closed circular templates and generates more circles. In the late phase, replication by a rolling-circle mechanism generates multiple-length λ DNA molecules, which serve as substrates for encapsidation. In contrast to lytic growth, some derivatives of λ can replicate indefinitely as circular plasmid DNA molecules.

The phage and host gene products essential for λ DNA replication are listed in Table 1. Most of the host requirements have been identified by challenging λ to replicate at the nonpermissive temperature in Escherichia coli mutants temperature-sensitive for replication of the bacterial chromosome. With the important exception of some functions thought to participate specifically in initiation at the E. coli replication origin, λ utilizes most of the replication machinery of its host. These proteins presumably carry out similar functions in the synthesis of λ DNA as they do in bacterial replication (for present understanding of biochemistry and control of DNA replication, see Kornberg 1980for present understanding of biochemistry and control of DNA replication, see Kornberg 1982). Only two...