Initiation and Termination of Chromosome Replication

Abstract

In this chapter, emphasis is on the processes of initiation and termination of replication of the B. subtilis chromosome. As an introduction to the discussion of these topics, a brief account is given of the work that has afforded a general picture of the topology of the B. subtilis chromosome through the three phases of the replication cycle. This account will be followed by a description of currently identified DNA replication genes in B. subtilis and a summary of what is known about the enzymology of the elongation phase of DNA replication in this organism. Initiation of bacterial chromosome replication was first defined as the step that requires synthesis of new proteins, while elongation proceeds to completion without concomitant synthesis of proteins. In this review, emphasis is also based on the universal mechanism commonly found in other bacterial species, particularly E. coli. The effect of a dnaB mutation on the two types of membrane-DNA complexes is described. The cycle of chromosome replication commences with initiation. Termination is defined here as the meeting and fusion of the forks to yield two separate and continuous double-stranded segments of DNA spanning the site of fusion. Termination of chromosome replication in E. coli also involves arrest of replication forks, which is effected by protein-DNA interactions analogous to those observed in B. subtilis.