Distribution of Bacteriophage +3T Homologous Deoxyribonucleic Acid Sequences in BaciZZus subtihs

The Bacillus subtilis 166 chromosome was found to share extensive homology with the genome of bacteriophage +3T. At least three different regions of the bacterial genome hvdridized to ribonucleic acid complementary to +3T deoxyribonucleic acid (DN.1). The thymidylate synthetase gene, thyA, of B. subtilis and the sequences adjacent to it were shown to be homologous to the region in the +3T DSA containing the phage-encoded thymidylate synthetase gene, thyP3. SP,f?, a temperate bacteriophage known to be integrated into the B. subtilis 168 chromosome, was demonstrated to be closelv related to 03T. Other regions of the bacterial genome were also found to hybridize to the +3T probe. The nature and location of these sequences in the bacterial and phage chromosomes were not identified. It was shown, however, that they were not homologous to either the th~P3 gene or the DXA surrounding the thyP3 gene. The chromosomes of other Bncillus species were also screened for the presence of +3T homologous sequences, and the th~P3 gene was localized in the linear genomes of phages 43T and pll by heteroduplex mapping. It is suggested that the presence of sequences of phage origin in the B. subtilis 168 chromosome might contribute to the restructuring and evolution of the viral and bacterial DNAs.