Rodriguez I R, Gonzalez P, Zigler J S, Borrás T
Laboratory of Mechanisms of Ocular Diseases, National Eye Institute, National Institutes of Health, Bethesda, MD 20892.
Biochim Biophys Acta. 1992 Oct 13;1180(1):44-52. doi: 10.1016/0925-4439(92)90025-i.
A congenital cataract present in guinea pigs provided a unique opportunity to study a hereditary lens disease at the molecular level. zeta-Crystallin, one of the most abundant guinea pig lens proteins, was found to be altered in the lens of cataractous animals. Several zeta-crystallin cDNA clones were isolated from a cataractous lens library and found to contain a 102-bp deletion towards the 3' end of the coding region. This deletion does not interfere with the reading frame but results in a protein 34 amino acids shorter. Sequence analysis of a normal genomic zeta-crystallin clone revealed that the missing 102-bp fragment corresponds to an entire exon (exon 7). PCR analysis of the genomic DNA isolated from cataractous animals showed that exon 7, though missing from the mRNA, is intact in the cataractous genome. Further sequence analysis of the zeta-crystallin gene disclosed a dinucleotide deletion of the universal AG at the acceptor splice-site of intron 6 of the mutant gene. The presence of this mutation results in the skipping of exon 7 during the mRNA processing which in turn results in the altered zeta-crystallin protein. This is the first time a genomic mutation in an enzyme/crystallin gene has been directly linked to a congenital cataract.
豚鼠中存在的先天性白内障为在分子水平研究遗传性晶状体疾病提供了独特的机会。ζ-晶体蛋白是豚鼠晶状体中含量最丰富的蛋白质之一，发现在患白内障动物的晶状体中发生了改变。从一个患白内障的晶状体文库中分离出了几个ζ-晶体蛋白cDNA克隆，发现它们在编码区的3'端含有一个102 bp的缺失。这种缺失并不干扰阅读框，但导致蛋白质缩短34个氨基酸。对正常基因组ζ-晶体蛋白克隆的序列分析表明，缺失的102 bp片段对应于一个完整的外显子（外显子7）。对从患白内障动物中分离的基因组DNA进行PCR分析表明，外显子7虽然在mRNA中缺失，但在患白内障的基因组中是完整的。对ζ-晶体蛋白基因的进一步序列分析揭示了突变基因内含子6的受体剪接位点处普遍存在的AG二核苷酸缺失。这种突变的存在导致在mRNA加工过程中外显子7的跳跃，进而导致ζ-晶体蛋白发生改变。这是首次将酶/晶体蛋白基因中的基因组突变与先天性白内障直接联系起来。
