Sequence of the genome of Salmonella bacteriophage P22

Abstract

The sequence of the nonredundant region of the Salmonella enterica serovar Typhimurium temperate, serotype-converting bacteriophage P22 has been completed. The genome is 41,724 bp with an overall moles percent GC content of 47.1%. Numerous examples of potential integration host factor and C1-binding sites were identified in the sequence. In addition, five potential rho-independent terminators were discovered. Sixty-five genes were identified and annotated. While many of these had been described previously, we have added several new ones, including the genes involved in serotype conversion and late control. Two of the serotype conversion gene products show considerable sequence relatedness to GtrA and -B from Shigella phages SfII, SfV, and SfX. We have cloned the serotype-converting cassette (gtrABC) and demonstrated that it results in Salmonella serovar Typhimurium LT2 cells which express antigen O1. Many of the putative proteins show sequence relatedness to proteins from a great variety of other phages, supporting the hypothesis that this phage has evolved through the recombinational exchange of genetic information with other viruses.

FIG. 1

ORFs and sequence similarity regions in P22 DNA. The ORFs for which no genetic designation had been made previously are labeled based upon the number of amino acid residues (e.g., ORF-80 would encode a protein with 80 amino acids). The striped and open boxes correspond to regions which have nucleic acid sequence similar to S. paratyphi A or coliphage λ DNA, respectively.

FIG. 2

Diagrammatic representation of the potential phylogenetic significance of similar proteins in P22 and other phages. The outermost level indicates those proteins that share >30% sequence identity. The genes on the map line correspond to proteins which share ≥60% identity, while the inner arrows refer to proteins which share ≥90% sequence identity. A single color is employed where the P22 protein has only a single homologue. In cases where similarity is to two proteins, the arrowhead and shaft are differently colored. Where homology is shared with ≥3 different phage proteins, the gene is represented in grey.