Sequence homology and recombination between the genomes of morphologically dissimilar bacteriophages LP 52 and theta.

A restriction fragment map of Bacillus licheniformis temperate phage LP 52 DNA (molecular weight 38.5 X 10(6)) was established, using restriction endonucleases BamHI (8 target sites), BglI (10 sites,) BglII (13 sites) and EcoRI (22 sites). The map is linear, with well-defined ends, without any signs of circular permutation. The DNA of a related phage, LP 51, produced identical restriction fragments. At least 62% DNA of LP 52 has been found homologous to the DNA of the recently discovered, morphologically quite dissimilar, phage I, as demonstrated by hybridization of electrophoretically separated restriction fragments of DNA. Under the same conditions, the DNAs of LP 52 and of the morphologically similar Bacillus subtilis phage phi 105 did not cross-hybridize. The homologous regions in the genomes of phages LP 52 and I have been shown to be colinear. Comparison of the cleavage maps of phages LP 52 and I has shown that, within the regions of homology, not a single restriction fragment and few restriction sites have been conserved during divergent evolution. Three major regions of heterology were defined; the longest one, covering the right-hand end of the map (73 +/- 2.75% up to 100% LP 52 genome length) appeared to contain genes coding for structural proteins of the virions; a shorter region at the left-hand end of the map (coordinates zero to 10.3 +/- 3.3% LP 52 genome length) and a very short central region (coordinates 41.8-43.9%) could be identified, the latter apparently containing a regulatory locus responsible for the heteroimmune behavior of the two phages. Recombinants between phages LP 52 and I were isolated. Mapping of recombinant genomes has indicated mutual substitution of allelic pieces of LP 52 and I DNAs upon strict conservation of overall genome length.

Restriction and modification in Bacillus subtilis 168. Regulation of hsrM(nonB) expression in spoOA mutants and effects on permissiveness for phi15 and phi105 phages.

Gene hsr M (nonB) of Bacillus subtilis 168, causing non-permissiveness to phage SP10 (Saito et al. 1979) and reduced plating efficiency of unmodified phage phi105, is responsible for non-permissiveness of B. subtilis 168 for phages phi15 and PZA. Upon transformation to sporulation deficiency (allele spoOA) B. subtilis 168 becomes permissive for phi15 and PZA and loses the ability to restrict phi105. spoOA str-1 double transformants of B. subtilis 168, however, retain the restriction 168 and non-permissiveness for phi15 and PZA phages, in spite of their Spo- phenotype. Therefore it appears that a functional product of the spoOA gene is required for expression of gene hsrM in wild-type bacteria, but is not essential in streptomycin-resistant bacteria. Phage genomes (PZA) were trapped in spores of the restriction deficient strain with much higher efficiency than in the wild-type.