CLONING OF SHV-2, OHIO-1, AND OXA-6 BETA-LACTAMASES AND CLONING AND SEQUENCING OF SHV-1 BETA-LACTAMASE

Molecular cloning of DNA fragments permitted the isolation of structural genes coding for SHV-1, SHV-2, OHIO-1, and OXA-6 β-lactamases. DNA probes were constructed for SHV-1, and under conditions of high stringency, hybridization was observed only between SHV-1 and SHV-2. Oligonucleotide typing with a 15-mer SHV-1 probe was capable of discriminating between SHV-1 and SHV-2 but not OHIO-1. The nucleotide sequence of the SHV-1 β-lactamase gene from plasmid R974 has been determined. The structural gene encodes a polypeptide product which differs by 9 residues from the p453 (SHV-1) PIT-2 enzyme determined by peptide sequencing. The significance of each mutation was assessed by alignment of amino acid sequences and comparisons with the Staphylococcus aureus PC1 penicillinase crystal structure. Structural similarities between SHV-1 and class A β-lactamases are extensive, with amino acid identities of 88.9% between SHV-1 and LEN-1, 91.8% between SHV-1 and OHIO-1, and 63.7% between SHV-1 and TEM-1.