Zeta-crystallin: a lens-specific promoter and the gene recruitment of an enzyme as a crystallin.

A novel enzyme with quinone oxidoreductase activity has undergone gene recruitment in certain mammals, acquiring a second function as the lens structural protein zeta-crystallin. Here we show that recruitment of this enzyme crystallin can be explained by the lens specificity of an alternative promoter which does not require host-specific factors. The strong lens preference of this promoter is apparent in both cultured cell transfections and in transgenic mice. While proximal regions of the promoter have some activity in the brain of transgenic mice this is abolished by the addition of more distal regions. The minimal active promoter is differentially footprinted by extracts from lens and non-lens cells. Deletion within the major region footprinted in lens, ZPE (zeta protected element), abolishes promoter function. This is the first example of a lens-specific promoter in an enzyme crystallin gene and the first demonstration of gene recruitment by this mechanism.