Regulation of Chromosome Replication in Bacillus subtilis

Sequential replication of bacterial chromosomes has been suggested from the pattern of DNA synthesis after amino acid deprivation from amino acid requiring mutants of E. coli (Maal~e, 1961). More direct evidence has recently been reported in different systems. In the Bacillus subtilis transformation system, the replication of different markers in B. subtilis does not occur in random-in-time fashion but has a regular oriented pattern (u and Sueoka, 1962, 1963a, 1963b). Nagata (1962, 1963) reported evidence of sequential replication of the E. coli chromosome by studying the pattern of duplication of ~ prophage in syn-chronized cultures of Hfr strains of E. coli K12. The unidirectional replication of E. coli chromo-somes was also demonstrated from a radioauto-graphic study by Cairns (1963). In this paper, the data obtained in the B. subtilis system are summarized, and the more recent results will be presented. Thus, the replication of markers on the chromosomes of a strain (strain 23 of Burkholder and Giles, 1947) follows a defi-nite pattern, allowing construction of a genetic map of the entire chromosome. This polarity of chromosome r plication is not, however, found in another strain of B. subtilis (strain 168 of Burk-holder and Giles, 1947). The implication of this result to the regulation of chromosome r plication will be discussed