Y-box proteins interact with the S1 nuclease-sensitive site in the chicken alpha 2(I) collagen gene promoter.

The sequence of the chicken alpha 2(I) collagen promoter from -712 to -85, relative to exon 1, has been shown to be important for transcriptional activity. Within this region a pyrimidine/purine asymmetrical element at -200 bp forms an in vitro S1 nuclease-sensitive site. The pyrimidine-rich strand of this element interacts specifically with single-stranded DNA-binding proteins present in fibroblast nuclear extracts [Bayarsaihan and Lukens (1996) Biochem. J. 314, 293-296]. To identify these proteins we performed expression screening of a chick embryo fibroblast cDNA library using a single-stranded polypyrimidine sequence derived from this element. One of the isolated clones was found to encode a member of the cold-shock gene family, either chicken YB-1 or a highly homologous protein. This protein and a known chicken Y-box protein were both found to bind sequence-specifically to the pyrimidine-rich strand of the pyrimidine/purine asymmetrical element in the chicken alpha 2(I) collagen promoter. The binding mechanism of these proteins could be based on the formation of a non-canonical triplex DNA structure (H-DNA). Although members of this widespread and conserved protein family have been reported to modulate the expression of a number of genes, the findings reported here provide the first evidence for a possible role of cold-shock proteins in the regulation of type I collagen genes.