IS 257 from Staphylococcus aureus: member of an insertion sequence superfamily prevalent among Gram-positive and Gram-negative bacteria

Abstract

The nucleotide sequences for the IS 257 family of insertion sequences from Staphylococcus aureus were compared with those of the ISS 1 family from Streptococcus lactis and the IS 15 family which is widespread amongst Gram-negative bacteria. These elements have a striking degree of similarity in both their putative transposase polypeptide sequences and their nucleotide sequences (40 to 64% between pairs), including 12 out of 14 bp conservation in their terminal inverted repeats. The evolutionary distance between the IS 15 family and the IS 257 and ISS 1 families of Gram-positive origin is approximately twice that between the IS 257 and ISS 7 families. Analysis of base substitutions in the three sequences has provided insights into the effect of selection for the G + C content of immigrant genes to conform to that of their hosts, and into the evolution of biases in overall amino acid composition of cellular proteins in prokaryotes and eukaryotes. The IS 257, ISS 7, IS 75 families form a superfamily of insertion sequences that has been involved in the spread of a number of antimicrobial resistance determinants in Gram-positive and Gram-negative pathogens.