A pyrimidine element with mirror repeats centred at position -192 bp of the chick α2(I) collagen promoter interacts with sequence-specific DNA-binding factors. These factors bind to only the pyrimidine strand of this region and have no affinity for the complementary purine strand. Binding activity is also seen with the double-stranded form of this element, but with less affinity than to the single-stranded pyrimidine species. Southwestern blot analyses have shown that proteins of 80 and 134 kDa in chick embryo fibroblast nuclear extracts bind to the pyrimidine strand, whereas only a 134 kDa DNA-binding protein was found in chondrocyte nuclear extracts. The binding mechanism of these nuclear proteins with single-stranded DNA might be based on a non-B-DNA conformation of the pyrimidine element. The position of this binding site in the promoter region, its potential for adopting an unusual secondary structure and the presence of the 80 kDa binding factor in chick embryo fibroblasts, but not in chondrocytes, suggest a possible role for this factor in the expression of the α2(I) collagen gene.
Fine structural analysis of the human pro-alpha 1 (I) collagen gene. Promoter structure, AluI repeats, and polymorphic transcripts.