Molecular and biochemical analysis of AST-1, a class A beta-lactamase fromNocardia asteroides sensu stricto

A beta -lactamase gene was cloned from a Nocardia asteroides sensu stricto clinical isolate. A recombinant plasmid, pAST-1, expressed the beta -lactam ase AST-1 in Escherichia coli JM109, Its pI was 4,8, and its relative molec ular mass was 31 kDa, E, coli JM109(pAST-1) was resistant to penicillins an d narrow-spectrum cephalosporins, The beta -lactamase AST-1 had a restricte d hydrolytic activity spectrum. Its activity was partially inhibited by cla vulanic acid but not by sulbactam and tazobactam. AST-1 is an Ambler class A beta -lactamase sharing 65% amino acid identity with beta -lactamase FAR- 1, the most closely related enzyme.