A gene from Alcaligenes denitrificans that confers albicidin resistance by reversible antibiotic binding

Albicidin antibiotics specifically block prokaryote DNA replication. The albicidin resistance gene (albB) cloned from a soil isolate of Alcaligenes denitrificans encodes a 23 kDa protein capable of detoxifying albicidin by reversible binding. This mechanism operates intracellularly to protect DNA replication in albicidin-sensitive Escherichia coli expressing the cloned resistance gene, which can be induced fivefold in the presence of 1.5 micrograms albicidin ml-1 in the surrounding medium. The coding region of 621 bp has regions with partial DNA sequence homology to an albicidin resistance gene (albA) from Klebsiella oxytoca, but with rearrangements and frame-shifts resulting in loss of protein homology. There is a short region of N-terminal homology between the albicidin resistance (Albr) proteins from A. denitrificans and K. oxytoca, although the two genes use different codons for shared amino acids. The N-terminal homology suggested a common functional domain; this was confirmed by deletion analysis, translational fusions and albicidin binding by a synthetic oligopeptide. Antibiotic binding provides a high level of albicidin resistance in E. coli. The gene appears to be a useful candidate for transfer to plants to protect plastid DNA replication from inhibition by albicidin phytotoxins involved in sugarcane leaf scald disease.