Cloning and characterization of an albicidin resistance gene from Klebsiella oxytoca.

A DNA fragment containing a gene for resistance to the antibiotic albicidin was isolated from Klebsiella oxytoca and shown to be expressed in Escherichia coli, where it also protected bacteriophage T7 replication from inhibition by albicidin. In vivo translation analysis demonstrated that the cloned 2.2kb DNA fragment coded for a 36 kiloDalton (kD) protein and a 25kD protein. The DNA sequence was determined for a 654-base-pair open reading frame contained within a 1.2kb subcloned DNA fragment encoding albicidin resistance. The predicted molecular weight of the polypeptide translated from the open reading frame was 25.8kD. A putative Shine-Dalgarno sequence precedes the open reading frame but a potential promoter sequence was not detected. A possible rho-independent transcription termination signal was found directly following the stop codon. The functional protein for albicidin resistance was isolated and purified. Both the molecular weight and NH2-terminal amino acid sequence of this protein correspond with that predicted from the DNA sequence of the open reading frame. The cloned albicidin resistance gene had no effect on the tsx (nupA) nucleoside uptake gene associated with spontaneous albicidin resistance in E. coli; also, it did not complement any of a range of E. coli DNAts mutants at restrictive temperatures. The cloned resistance gene product remained intracellular in exponential cultures of K. oxytoca and E. coli. Cell-free extracts from E. coli containing the resistance gene protected a sensitive strain of E. coli from inhibition by albicidin, as did the purified albicidin resistance protein. The mechanism of this albicidin resistance protein involved binding to albicidin to form a complex without antibiotic activity, but without catalysing further chemical modification of the antibiotic.