Abstract
Abstract
Little is known about the roles of the 16 extracytoplasmic function (ECF) sigma factors in Rhodopseudomonas palustris gene regulation. To begin to address this deficiency, the whole proteome of R. palustris CGA010 was analyzed by tandem mass spectrometry from cultures episomally expressing the ECF ��RPA4225. Among the proteins with the greatest increase in abundance were the catalase KatE, trehalose synthase, a DPS-like protein, and several regulatory proteins. Alignment of the cognate promoter regions driving expression of several up-regulated proteins revealed a conserved binding motif in the -35 and -10 regions with the consensus sequence GGAAC-18N-TT. Analysis of the genome revealed the occurrence of this motif in the promoters of over 150 genes, including general stress proteins, ATP-dependent DNA ligase, two Ku-domain-containing proteins, and the heat-shock �m factor rpoH. Additionally, the putative anti-�m factor RPA4224, whose gene is contained in the same predicted operon as RPA4225, was identified as interacting directly with the predicted response regulator RPA4223 by mass spectrometry of affinity isolated protein complexes. Furthermore, another protein containing a cytoplasmic histidine kinase domain is located immediately upstream of RPA4225. The genomic organization of homologues for these four genes is conserved in several other strains of R. palustris as well as in closely related �\-proteobacteria. Taken together, these data suggest that ECF ��RPA4225 controls a global stress regulon that is in turn controlled via a phosphorelay mechanism involving a histidine kinase sensor, a response regulator, and an anti �m factor that are conserved among several members of �\-proteobacteria.
