Nuclotide sequence and organization ofdnaBgene and neighbouring genes on theBacillus subtilischromosome

A region of the Bacillus subtilis chromosome containing dnaB, a gene essential for the initiation of chromosomal replication in B. subtilis, was cloned and nucleotide sequence of some 5000bp determined. The region consists of 4 open reading frames (ORFs) possibly comprising a single transcriptional unit. Two dnaB mutations, dnaB27 and dnaB19 were located within the first ORF which would give rise to a protein of 472 amino acids. The dnaB27 mutation involves codon at the position of 122 (replacement of Asp by Asn) close to a DNA binding domain and the dnaB19 codon 379 (replacement of Ala by Thr) close to a region rich in charged amino acids which may be alpha helical. The third ORF in the same transcriptional unit would produce a hydrophobic protein which might be involved in the DNA-membrane binding function of dnaB gene. No homologous Escherichia coli genes have been found.