OVERLAPPING POSITIVE AND NEGATIVE REGULATORY ELEMENTS DETERMINE LENS-SPECIFIC ACTIVITY OF THE DELTA-1-CRYSTALLIN ENHANCER

Lens-specific expression of the delta1-crystallin gene is governed by an enhancer in the third intron, and the 30-bp-long DC5 fragment was found to be responsible for eliciting the lens-specific activity. Mutational analysis of the DC5 fragment identified two contiguous, interdependent positive elements and a negative element which overlaps the 3'-located positive element. Previously identified ubiquitous factor deltaEF1 bound to the negative element and repressed the enhancer activity in nonlens cells. Mutation and cotransfection analyses indicated the existence of an activator which counteracts the action of deltaEF1 in lens cells, probably through binding site competition. We also found a group of nuclear factors, collectively called deltaEF2, which bound to the 5'-located positive element. DeltaEF2a and -b were the major species in lens cells, whereas deltaEF2c and -d predominated in nonlens cells. These deltaEF2 proteins probably cooperate with factors bound to the 3'-located element in activation in lens cells and repression in nonlens cells. DeltaEF2 proteins also bound to a promoter sequence of the gammaF-crystallin gene, suggesting that deltaEF2 proteins are involved in lens-specific regulation of various crystallin classes.