Analysis of the terminus region of the Bacillus subtilis chromosome

Abstract

Considerable progress has been made in the chemical characterization of the origin of replication of the bacterial chromosome in both Escherichia coli and Bacillus subtilis^1–4. This region is important in the initiation and control of replication. The replication terminus, or position at which the two replication forks meet, is located opposite the origin, but its structure is unknown despite its several interesting properties which, almost certainly, reflect a significant biological role in the overall cell cycle—it seems to inhibit the movement of replication forks^5,6, it is remarkably devoid of genetic information^7,8 and, like the origin, it shows a specific interaction with the cell surface, probably the membrane⁹. Recently, it was shown that the sporulation process in B. subtilis could be used to label the bacterial chromosome terminus radioactively^10,11. Here we have investigated the number and nature of the labelled DNA fragments generated by restriction endonuclease treatment of chromosomes labelled over progressively shorter distances in the vicinity of the terminus. The results show that termination of B. subtilis chromosome replication is a more specific process than it has hitherto been possible to establish. Furthermore, the findings open the way to structural studies on the terminus region and to an examination by a very direct approach of the movement of replication forks within it.