Synthesis of R plasmid coded β lactamase in minicells and in an in vitro system

Abstract

β-Lactamase encoded by a small, nontransferring R-plasmid, NTP1, conferring ampicillin resistance to its host bacteria, was purified. NTP1 plasmid-coded β-lactamase was found to be periplasmically located in the host E. coli cell, to have a molecular weight of about 25,000, and to show a relatively low activity against oxacillin and methicillin compared with benzylpenicillin. These characteristics indicate that NTP1 plasmid-coded β-lactamase is very similar or identical to the 'TEM-type' β-lactamase, which is the most common β-lactamase coded by R-plasmids in enteric bacteria. In minicells containing NTP1 plasmids, at least six plasmid-specific proteins were synthesized, and β-lactamase was synthesized in agreater amount than other plasmid-coded proteins. In a cell-free transcription-translocation coupled system from E. coli, NTP1 plasmid deoxyribunucleic acid directed the synthesis of several species of plasmid-specific proteins, including active β-lactamase. The in vitro system also showed preferential synthesis of β-lactamase, as was observed in minicells containing NTP1 plasmids.