CHARACTERIZATION OF TRANSCRIPTION ORGANIZATION AND ANALYSIS OF UNIQUEEXPRESSION PATTERNS OF AN ALKYL HYDROPEROXIDE REDUCTASE C GENE (AHPC)AND THE PEROXIDE REGULATOR OPERON AHPF-OXYR-ORFX FROM XANTHOMONAS-CAMPESTRIS PV PHASEOLI

We have analyzed the transcription organization of ahpC, ahpF, oxyR, a nd oxfX from Xanthomonas campestris pv, phaseoli, ahpC was transcribed as a monocistronic 0.6-kb mRNA, while ahpF-oxyR-orfX were transcribed as a polycistronic approximately 3.0-kb-long mRNA, The novel transcri ption organization of these genes has not observed in other bacteria. Western analysis showed that oxidants (peroxides and superoxide anions ), a thiol reagent (N-ethylmaleimide), and CdCl2 caused large increase s in the steady-state level of AhpC, Growth at alkaline pH also modera tely induced AhpC accumulation. Thermal and osmotic stresses did not a lter the levels of AhpC. Northern blotting results confirmed that oxid ant- and CdCl2-induced AhpC accumulation was due to increased levels o f ahpC transcripts. Analysis of oxyR expression revealed a unique patt ern. Unlike other bacterial systems, peroxides and a superoxide genera tor induced accumulation of OxyR. Northern blotting results confirmed that these oxidants induced expression of oxyR operon, This novel regu latory pattern could be generally important. The transcription organiz ation and patterns of chemicals and stress induction of ahpC and oxyR differed from those of other bacteria and are likely to be important f or X. campestris pv, phaseoli survival during exposure to oxidants.