A novel subsp. mutant designated RexZ, (egulator of oenzymes) showed reduced production of the degradative exoenzymes. The gene product shows similarity to the KdgR regulatory protein from , described as the major repressor of the pectin catabolism pathway genes in the latter species. DNA—protein interaction experiments demonstrated that the synthesis of the RexZ protein is controlled by the cAMP—CRP (cAMP—receptor protein) complex. Western blot analysis also revealed the presence of a second KdgR homologue (distinct from RexZ) which, like RexZ, was present in all species of the genus tested. The corresponding KdgR proteins from both subsp. and subsp. share a high level of sequence identity with the KdgR homologues from and Although the subsp. regulatory region displayed specific interactions with both the purified KdgR repressor and the partially purified subsp. KdgR, quantification revealed that the cellular level of RexZ protein was unaffected by the presence of pectic compounds. This study shows that the complex regulatory network governing virulence in the erwinias involves two totally distinct, but highly conserved, members of the IcIR class of DNA binding proteins: RexZ and KdgR.


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