Comparison of Bacillus subtilis phages PZA, phi 29 and phi 15

Morphologically identical phages PZA, PZE , phi 29, and phi 15 can be distinguished by the neutralization test with rabbit antisera and by host range specificity. Each member of this phage group contains 18 kb double-stranded linear DNA carrying proteins covalently attached to its 5' ends. Physical maps of their DNA constructed with the use of restriction endonucleases EcoRI, HpaI, HindIII, BspRI, and XbaI and DNA-DNA hybridization experiments show a closer relationship between phi 29 and PZE than between phi 29 and phi 15 or phi 29 and PZA. phi 15 is closer to PZA than to phi 29. This conclusion is supported by analysis of differential denaturation profiles of the phage DNAs. Sequencing of selected parts of phi 29 and PZA DNAs reveals 93% homology with a preference for synonymous base replacements (silent mutations) randomly distributed in the coding regions. Using promoter-probe plasmid pPV33 -H the region functioning as a promoter in E. coli was localized on the smallest EcoRI fragment of PZA and phi 29 DNAs. Comparison of the nucleotide sequence of this region with known promoters of B. subtilis shows extensive homologies with at least two types of promoters of different specificities, namely those recognized by factors sigma 28 of B. subtilis and sigma gp28 of phage SPO1 . These promoter-like regions overlap and the whole sequence is conserved in both phages.