DIFFERENTIAL-EFFECTS OF DNA-BINDING PROTEINS ON BIDIRECTIONAL TRANSCRIPTION FROM THE COMMON PROMOTER REGION OF HUMAN COLLAGEN TYPE-IV GENESCOL4A1 AND COL4A2

Expression of the heterotrimeric collagen IV (alpha1(IV))2alpha2(IV) i s essential for the structural integrity and functional properties of basement membranes. The genes COL4A1 and COL4A2 coding for both subuni ts are located close to each other on the same chromosome and are tran scribed from a common bidirectional promoter element. Binding of at le ast three different nuclear proteins could be detected within this pro moter, a CCAAT-binding protein, Spl and a newly identified factor, des ignated 'CTCBF'. Mutagenesis of binding sites proved that these factor s are essential for the efficient transcription of both genes, but rev ealed differential gene-specific effects. Therefore, the common promot er region of collagen IV does not represent an equally functional bidi rectional element, but may be better understood as two overlapping gen e-specific promoters with shared elements.