Bacteriophage B103: complete DNA sequence of its genome and relationship to other Bacillus phages

The genome of Bacillus subtilis bacteriophage B103 consists of double-stranded linear DNA 18 630 bp long. The DNA was sequenced, and the sequence was compared with DNA sequences of closely related phages, namely the members of the phage ϕ29 family. Among them, phage Nf was shown to be the most closely related to B103. Comparisons of several open reading frames (ORFs) among the familly members helped to identify genes 1 and 5. A cluster of ORFs between genes 16 and 17 contains two ORFs with partial homology with two ϕ29 ORFs located in the same region. There are three more ORFs in this region of B103 with good ribosome binding sites (RBS) and optimal codon usage that are not homologous to any of the ϕ29 ORFs. The function of these five ORFs remains unexplained. It was shown that major promoters characterized in ϕ29 are retained in B103. Where many substitutions occur in the vicinity of a promoter, at least the −10 and −35 boxes are conserved.