Elements in the first intron of the alpha 1(I) collagen gene interact with Sp1 to regulate gene expression.

Sequences within the first intron of the alpha 1(I) collagen gene act both positively and negatively to regulate expression of the gene. We have further characterized a 274 bp intronic sequence that contains an orientation-specific inhibitory activity and represents a constitutive DNase I-hypersensitive site in the gene. We show that this sequence contains two tandem, unique binding elements for the transcription factor Sp1. In addition, an Sp1-like site, capable of competing for protein binding to the intronic elements, resides in the distal promoter of the collagen gene. The results of experiments with site-directed mutations that abolish binding to the intronic elements indicate that these protein-DNA interactions have an inhibitory effect on the transcriptional efficiency of alpha 1(I) collagen-reporter gene constructs in transient transfection analysis. These data support our conclusion that the first intron plays a complex role, involving multiple protein-DNA binding interactions, in the regulation of expression of the alpha 1(I) collagen gene.