Interaction of the main cold shock protein CS7.4 (CspA) of Escherichia coli with the promoter region of hns.

Escherichia coli protein CS7.4 (CspA), homologous to the class of eukaryotic Y-box DNA-binding proteins, is a cold shock transcriptional activator of at least two genes, hns and gyrA. It was demonstrated that all or nearly all the elements necessary for the stimulation of hns transcription by CS7.4 protein are located in the proximal 110 bp DNA fragment of this gene with no additional elements being present in a longer fragment (660 bp) extending further upstream from the hns promoter. Protein CS7.4 bound strongly to the 110 bp segment of the hns promoter in crude extracts of cold shocked cells, but the purified protein displayed a weak interaction with the same DNA fragment. Purified CS7.4 protein also caused increased or decreased accessibility to DNase I at different sites of the 110 bp fragment of hns but the majority of these effects was seen only in the presence of RNA polymerase. Since gel shift experiments showed that protein CS7.4 stimulated the binding of RNA polymerase to the promoter of hns and since it is known that there are similarities between CS7.4 and ssDNA-binding proteins, we suggest that formation of the open complex by the RNA polymerase or protein-protein contacts between CS7.4 and the RNA polymerase are prerequisites for and/or the effects of the interaction of CS7.4 with its DNA target. The presence of a conserved CCAAT element in the hns promoter region, on the other hand, was found not to be stringently required for cold shock activation since expression of E coli of an hns-cat fusion containing the Proteus vulgaris hns promoter lacking a CCAAT box increased over four-fold after cold shock.