SPECIFICITIES OF FEMA AND FEMB FOR DIFFERENT GLYCINE RESIDUES - FEMB CANNOT SUBSTITUTE FOR FEMA IN STAPHYLOCOCCAL PEPTIDOGLYCAN PENTAGLYCINE SIDE-CHAIN FORMATION

The femAB operon codes for two nearly identical similar to 50-kDa prot eins involved in the formation of the staphylococcal pentaglycine inte rpeptide bridge. Sequencing and analysis of the femA region of mutants isolated by chemical mutagenesis and selection for lysostaphin resist ance revealed point mutations leading to the expression of truncated F emA proteins. These femA mutants, although still producing an intact F emB, exhibited a phenotype identical as that described for femAB doubl e mutants. Thus, FemA seems to be essential for the addition of glycin e residues 2 and 3 only, whereas FemB is involved in the attachment of exclusively glycine residues 4 and 5. Although FemB has 39% identity with FemA, it cannot substitute for FemA. The FemA and FemB proteins s eem to be highly specific in regard to the position of the glycine res idues that they attach.