The locus for the hereditary human Coppock-like cataract (CCL) is closely linked to a particular combination of polymorphic Taql sites within the human 7-crystallin gene cluster. Mapping of these sites shows that they define a 15 kb region encompassing the ΓD and ψΓE gene. The ΓD and the ψΓE gene were cloned from the CCL chromosome and characterized. The ΓD gene was functionally equivalent to its allele cloned from a wild-type chromosome. The CCL ψΓE gene contains a cluster of sequence changes within and around its TATA box. Together these cause a ten-fold increase in the activity of the ψΓE promoter, raising the level of expression of this gene to 30% of that of the ΓD gene. The predicted protein product of the ψΓE gene is a 6 kD N-terminal Γ-crystallin fragment.Reactivation of the ψΓE gene and concomitant overexpression of the Γ-crystallln fragment could be the cause of the Coppock-like cataract.