Disassociation of σ subunit from RNA polymerase of Xanthomonas oryzae pv. oryzae by phage Xp10 infection

The σ subunit of Xanthomonas oryzae pv. oryzae is disassociated from host RNA polymerase after phage Xp10 infection. To clarify the possible mechanism for this observation, σ subunit was purified and an antiserum against σ subunit was prepared. Immunoprecipitation of RNA polymerase by the anti-core RNA polymerase antiserum, followed by immunoblotting with anti-σ subunit antibody, revealed that σ subunit was lost from RNA polymerase within 10 minutes after Xp10 infection. Loss of σ subunit was not observed under other stress conditions including heat and cold stress, starvation and growth to stationary phase. Two-dimensional immunoblotting analysis did not reveal any covalent modification of either σ subunit or RNA polymerase after Xp10 infection. These results suggest that separation of σ subunit from RNA polymerase may be due to competition with other binding factors.