Cell membrane and chromosome replication in Bacillus subtilis.

This review covers studies of the structural and functional roles of the cell membrane on the replication of the Bacillus subtillis chromosome. A particular emphasis is placed on the essential roles of the membrane complex for the in vivo initiation and termination of the chromosome replication. A critical gene complex in B. subtillis for the role of membrane complex is the dnaB operon that most likely consists of four genes (dnaB, dnaI, ORFZ/ORF213, and ORF omega/ORF281). Detailed studies of these genes are currently available only for the dnaB and dnaI genes. The unique feature of the dnaB gene is that temperature-sensitive mutants of this gene simultaneously lose, at the nonpermissive temperature, chromosome attachment at oriC to the membrane as well as the new round of replication initiation at oriC. Further studies on the genes and their products of the dnaB operon are therefore essential for our understanding of the in vivo mechanism of the initiation of chromosome replication and its regulation. The role of the membrane on the termination and segregation of the daughter chromosomes has not been discovered, but an important clue comes from the terminus area of the B. subtillis chromosome being bound to the membrane in a high-salt resistant and DnaB-independent fashion.