THE BLA GENE OF THE CEPHAMYCIN CLUSTER OF STREPTOMYCES-CLAVULIGERUS ENCODES A CLASS-A BETA-LACTAMASE OF LOW ENZYMATIC-ACTIVITY

A gene (bla) encoding a beta-lactamase is present in the cephamycin ge ne cluster of Streptomyces clavuligerus, the strain producing clavulan ic acid and a beta-lactamase inhibitory protein, The bin gene is locat ed 5.1 kb downstream from and in the opposite orientation to cefE, enc oding the deacetoxycephalosporin C synthase, The bla gene encodes a 33 2-residue protein (M-r, 35,218), similar to other class A beta-lactama ses produced by actinomycetes, Modification (to SDG) of the SDN conser ved motif of class A beta-lactamases as well as of amino acids in othe rwise conserved regions in the molecule may explain the low penicillin ase and cephalosporinase activities of the protein, The beta-lactamase has been purified to homogeneity and found to bind [H-3] benzylpenici llin, a result reflecting a rate-limiting deacylation step. Nucleotide sequences homologous to bla were found in all tested cephamycin produ cers, but several other Streptomyces species which produce a beta-lact amase do not contain genes for beta-lactam antibiotic biosynthesis.