RIFAMPICIN - AN INHIBITOR OF XP12-SPECIFIC PROTEIN-PHOSPHORYLATION INXANTHOMONAS-ORYZAE PV ORYZAE

Phosphorylation of the three Xp12-specific phosphoproteins was drastic ally reduced by rifampicin, an antibiotic that specifically inhibits t he host-cell RNA polymerase. However, this inhibitory effect could not be found in spontaneous mutants of Xanthomonas oryzae pv. oryzae whos e RNA polymerase are resistant to the drug. The inhibitory effect of r ifampicin treatment also resulted suppression of the Xp12 multiplicati on cycle. This implies the physiological significance of this effect a nd supports our previous prediction that phosphorylation plays an impo rtant role in the life cycle of Xp12. The acid- and alkali-labile char acter of the Xp12-specific phosphoproteins and the chemical stability of the phosphoryl linkages show that the corresponding protein kinase catalyzes the formation of an acyl phosphorylation. Subsequent fractio nation of cell lysate revealed that the phosphoproteins were located i n the periplasm. Actinomycin D, which affects transcription through DN A condensation rather than its binding to RNA polymerase, was not able to cause the inhibition effect. On the other hand, cerulenin was foun d to reduce the acyl phosphorylation which hints at a possible role of cell membrane in the phosphorylation. Here we present the evidence fo r the functional involvement of the rifampicin treatment on protein ph osphorylation. A possible mechanism of rifampicin on the alternation o f acyl phosphorylation is proposed.