Isolation and characterization of the gene encoding an aminopeptidase involved in the selective toxicity of ascamycin toward Xanthomonas campestris pv. citri.

An aminopeptidase gene named XAP has been isolated from Xanthomonas campestris pv. citri, a plant pathogenic bacterium. The bacterium is one of the rare micro-organisms susceptible to ascamycin, an aminoacyl nucleoside antibiotic that inhibits protein synthesis. Sequence analysis reveals that the gene encodes a 311 amino acid protein with a calculated molecular mass of 35134 Da and approx. 50% identity for amino acids to the proline iminopeptidase from Neisseria gonorrhoeae. The XAP gene product, Xap, expressed in Escherichia coli has proline iminopeptidase activity as well as ascamycin dealanylating activity in vitro.