The sequence of infB, encoding the prokaryotic translation-initiation factor 2 (IF2), was determined in eight strains of Streptococcus agalactiae (group B streptococcus) and an alignment revealed limited intraspecies diversity within S. agalactiae. The amino acid sequence of IF2 from S. agalactiae and from related species were aligned and revealed an interspecies conserved central and C-terminal part, and an N-terminal part that is highly variable in length and amino acid sequence. The diversity and relationships in a collection of 58 genetically distinct strains of S. agalactiae were evaluated by comparing a partial sequence of infB. A total of six alleles were detected for the region of infB analysed. The alleles correlated with the separation of the same strains of S. agalactiae into major evolutionary lineages, as shown in previous work. The partial sequences of infB were furthermore used in phylogenetic analyses of species closely related to S. agalactiae, yielding an evolutionary tree which had a topology similar to a tree constructed using 16S rRNA sequences from the same species.
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Investigation of the translation-initiation factor IF2 gene, infB, as a tool to study the population structure of Streptococcus agalactiaeThe EMBL accession numbers for the sequences reported in this paper are AJ003164 and AJ251493 to AJ251499.