ABSTRACT
Chromosomal organization in related temperate Bacillus subtilis bacteriophages SP beta, phi 3T, rho 11, Z, and E was compared. DNA-DNA hybridization studies done in conjunction with available restriction fragment maps of SP beta, phi 3T, and rho 11 demonstrated that DNA homology between these three phages extended over most of their respective genomes, although each contained unique chromosomal segments, phi 3T, rho 11, Z, and E, but not SP beta, possessed apparently homologous structural genes (thyP) for thymidylate synthetase. DNA from all thyP-containing phages transformed thymine auxotrophs of B. subtilis SP beta lysogens to prototrophy. This transformation commonly involved incorporation of the thyP gene into SP beta prophage within a region corresponding to the middle of the viral chromosome. Chimeric plasmids containing the thyP gene from phi 3T or cloned fragments of SP beta DNA were used in DNA-DNA hybridization studies to locate the thymidylate synthetase gene near the center of the phi 3T chromosome, and to demonstrate that the organization of this region resembled the analogous portion of the SP beta genome. Profiles of virion structural proteins from the five phages were also very similar, further suggesting functional homology between these viruses. However, despite these evidences of relatedness, populations of fragments generated by digesting SP beta, phi 3T, rho 11, Z, and E DNA with restriction enzymes were quite dissimilar.
Subject(s)
Bacteriophages/genetics , DNA, Viral/genetics , Genes, Viral , Bacillus subtilis/metabolism , Bacteriophages/analysis , DNA Restriction Enzymes , DNA, Viral/analysis , Lysogeny , Nucleic Acid Hybridization , Sequence Homology, Nucleic Acid , Thymidylate Synthase/genetics , Thymine/biosynthesis , Viral Proteins/analysisABSTRACT
The central portion of the chromosome of temperate Bacillus subtilis bacteriophage SPB was found to contain a region in which large deletions occurred, sometimes at high frequency. Most of the deletions could be placed into one of three groups, del1, del3, and del4, which were missing 11.8, 14.2, and 14 kilobase pairs of DNA, respectively. The chromosomal positions of the three types of deletions overlapped and together defined a continuous region of 27 kilobase pairs surrounding the prophage attachment site attPSPB. The 27-kilobase-pair segment contained no functions required for lytic growth of the phage, but DNA within this region was used as a template for RNA synthesis at several stages in the life cycle of SPB. In addition the transcription of DNA during lytic infection was found to be initiated over a large portion of one-half of the viral chromosome (the arbitrary left half). Subsequently, the synthesis of early RNA was terminated as late transcription continued on the opposite side of the chromosome.
Subject(s)
Bacillus subtilis/genetics , Bacteriophages/genetics , DNA, Viral/genetics , Chromosome Deletion , DNA Restriction Enzymes , DNA, Bacterial/genetics , Gene Expression Regulation , Lysogeny , Mutation , RNA, Viral/genetics , Transcription, Genetic , Transformation, GeneticABSTRACT
Thymine auxotrophs of Bacillus subtilis strains lysogenic for temperate bacteriophage SP beta c2 were transformed to prototrophy by DNA from related phage phi 3T. During transformation, the phi 3T-encoded thymidylate synthetase gene, thyP3, became integrated into the extreme right end of the SP beta c2 prophage near the bacterial citK gene. Upon heat induction, the transformed B. subtilis cells released SP beta c2T phages that could lysogenize thymine auxotrophs and convert them to prototrophy. Comparison of restriction endonuclease fragments of DNAs from SP beta c2 and SP beta c2T phages revealed that the latter contained a large region of deletion and substitution near the center of the chromosome. This region included the phage attachment site on the SP beta c2 genome.
