Identification and molecular characterization of a gene homologous to epr (endopeptidase resistance gene) in Staphylococcus aureus.

Certain Staphylococci possess a gene called epr or lif that renders the cells resistant to lysis by glycylglycine endopeptidase. The resistance is conferred by modifying the amino acid composition of interpeptide chains in cell-wall peptidoglycan by increasing serine content and decreasing glycine content. A gene homologous to epr/lif was cloned from S. aureus RN450 genomic libraries and designated eprh. eprh was found to localize 27bp downstream of a novel cell-wall hydrolase gene lytN, which is in the same orientation with eprh. By analogy with epr/lif, eprh is suggested to be involved in the transfer of certain amino acids, possibly serine or amino acids other than glycine, to interpeptide chains of cell-wall peptidoglycan. Unlike epr/lif, overexpression of eprh in S. aureus did not result in an increased resistance to lysostaphin. Insertional inactivation of eprh or lytN by Campbell-type integration did not affect the susceptibility of the cells to lysostaphin, either. These results suggest that eprh and lytN are not essential genes for S. aureus growth. The physiological function of eprh remains unknown.