Zeta-crystallin: a lens-specific promoter and the gene recruitment of an enzyme as a crystallin.
ABSTRACT 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.
Article: Inability of chaperones to fold mutant zeta crystallin, an aggregation-prone eye lens protein.[show abstract] [hide abstract]
ABSTRACT: zeta-crystallin is a quinone oxido-reductase, recruited in the eye lens of hystricomorphic rodents and camels. A deletion mutation constituting the NADPH-binding domain causes congenital cataract in a strain of guinea pigs. The presence of large quantities of a-crystallin, a molecular chaperone, does not provide any protection against this. In order to investigate whether the underlying reason for the lack of protection is the formation of a folding-incompetent protein, we have expressed the mutant protein in a heterologous system along with other known chaperones. We expressed the mutant zeta-crystallin in E. coli along with other chaperones such as GroEL/ES and DnaK/DnaJ/GrpE and then analyzed whether these chaperones could increase the amount of protein partitioning into the soluble fraction of E. coli cells. These chaperones were unable to rescue the mutant protein from partitioning into inclusion bodies, although they could increase the yield of soluble wild-type zeta-crystallin. The deletion of 34 amino acids, constituting the NADPH-binding domain of zeta-crystallin, makes the protein incompetent to fold correctly and thus form insoluble aggregates. It perhaps suggests why the mutant strain of guinea pigs have cataract at birth even though their lenses contain high amounts of alpha-crystallin. This study also shows that certain mutations can render proteins incompetent to fold into soluble molecules despite abundant assistance.Molecular vision 12/2000; 6:232-6. · 2.20 Impact Factor
Article: Lens-specific gene recruitment of zeta-crystallin through Pax6, Nrl-Maf, and brain suppressor sites.[show abstract] [hide abstract]
ABSTRACT: Zeta-Crystallin is a taxon-specific crystallin, an enzyme which has undergone direct gene recruitment as a structural component of the guinea pig lens through a Pax6-dependent mechanism. Tissue specificity arises through a combination of effects involving three sites in the lens promoter. The Pax6 site (ZPE) itself shows specificity for an isoform of Pax6 preferentially expressed in lens cells. High-level expression of the promoter requires a second site, identical to an alphaCE2 site or half Maf response element (MARE), adjacent to the Pax6 site. A promoter fragment containing Pax6 and MARE sites gives lens-preferred induction of a heterologous promoter. Complexes binding the MARE in lens nuclear extracts are antigenically related to Nrl, and cotransfection with Nrl elevates zeta-crystallin promoter activity in lens cells. A truncated zeta promoter containing Nrl-MARE and Pax6 sites has a high level of expression in lens cells in transgenic mice but is also active in the brain. Suppression of the promoter in the brain requires sequences between -498 and -385, and a site in this region forms specific complexes in brain extract. A three-level model for lens-specific Pax6-dependent expression and gene recruitment is suggested: (i) binding of a specific isoform of Pax6; (ii) augmentation of expression through binding of Nrl or a related factor; and (iii) suppression of promoter activity in the central nervous system by an upstream negative element in the brain but not in the lens.Molecular and Cellular Biology 04/1998; 18(4):2067-76. · 5.53 Impact Factor