Deletion analysis of the essentiality of penicillin‐binding proteins 1A, 2B and 2X of Streptococcus pneumoniae

An internal fragment from each of the penicillinebinding protein (PBP) 1A, 2B and 2X genes of Streptococcus pneumoniae, which included the region encoding the active‐site serine residue, was replaced by a fragment encoding spectinomycin resistance. The resulting constructs were tested for their ability to transform S. pneumoniae strain R6 to spectinomycin resistance. Spectinomycin‐resistant transformants could not be obtained using either the inactivated PBP 2X or 2B genes, suggesting that deletion of either of these genes was a lethal event, but they were readily obtained using the inactivated PBP 1A gene. Analysis using the polymerase chain reaction confirmed that the latter transformants had replaced their chromosomal copy of the PBP 1A gene with the inactivated copy of the gene. Deletion of the PBP 1A gene was therefore tolerated under laboratory conditions and appeared to have little effect on growth or susceptibility to benzylpenicillin.