We have continued to characterize crystallin gene structure although greater emphasis was placed on expression. Sequences have been completed, or nearly completed, for the human and chicken alpha A- and the chicken beta B1-crystallin genes. Intron 1 of the human alpha A-crystallin gene has been shown to encode an insert exon found so far only in rodents. The 5' flanking sequence of the murine alpha A-crystallin gene has been dissected into a distal, enhancer-like element and a proximal element. Both elements bind specifically to different nuclear proteins of embryonic lens cells, as judged by gel retardation experiments. Transfection studies using the pSVOCAT expression plasmid have shown that the 5' flanking sequence of the chicken delta 1- crystallin gene contains an upstream region (-603 to -120) that appears to down-regulate promoter activity. Strong promoter activity has been identified in the 5' flanking sequence of the chicken beta B1-crystallin gene, initiating our efforts to study the regulation of this class of crystallins. The human and murine alphaB-crystallin genes haves been isolated; the promoter has been identified in the murine gene. A transgenic mouse facility has been established, and several progeny carrying hybrid genes using crystallin promoters have been born. Numerous crystallins have been shown to be enzymes: epsilon-crystallin is lactate dehydrogenase, delta-crystallin is argininosuccinate lyase and tau- crystallin is enolase, indicating the pragmatism of lens evolution, i.e., the use of enzymatic proteins in a new structural role. Finally, three crystallin polypeptides have been identified in the jellyfish lens; one (35K) has been purified and partially sequenced.
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