title: Molecular nature of a plasmid specifying beta-lactamase production in Haemophilus ducreyi.
abstract: We characterized pJB1, the plasmid previously reported to mediate beta-lactamase production in Haemophilus ducreyi. We studied its relationship to pMR0360 and RSF0885, the plasmids responsible for beta-lactamase production in Neisseria gonorrhoeae and Haemophilus parainfluenzae, respectively. Although pJB1 was maintained as a multicopy pool in Escherichia coli, it was not stably maintained in the absence of antibiotic selection. Electron microscope heteroduplex studies showed that it carried 100% of the transposable ampicillin resistance sequence TnA. This sequence was transposed to plasmid pUB307 at a low rate. Heteroduplexes between pMR0360 and pJB1 showed that they contained 3.3 megadaltons of homologous sequences. Two sets of nonhomologous sequences, one a TnA sequence and the other a non-TnA sequence, took the form of insertion loops. For plasmids pMR0360 and RSF0885, previously shown to be highly related, the nonhomologous sequences took the form of a substitution loop. We concluded that all three plasmids shared major portions of their sequences but differed in discrete segments. pJB1 was the first such plasmid to have a physically and functionally intact TnA sequence.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D001483:Base Sequence; D004262:DNA Restriction Enzymes; D004251:DNA Transposable Elements; D006190:Haemophilus / Q000235:genetics; D006191:Haemophilus ducreyi / Q000201:enzymology / Q000235:genetics*; D009344:Neisseria gonorrhoeae / Q000235:genetics; D009692:Nucleic Acid Heteroduplexes; D009693:Nucleic Acid Hybridization; D010957:Plasmids; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D009692:Nucleic Acid Heteroduplexes; D000667:Ampicillin; D004262:DNA Restriction Enzymes; D001618:beta-Lactamases