Winderickx J, Battisti L, Motulsky A G, Deeb S S
Department of Medicine, University of Washington, Seattle 98195.
Proc Natl Acad Sci U S A. 1992 Oct 15;89(20):9710-4. doi: 10.1073/pnas.89.20.9710.
The human red and green photopigments are specified by genes on the long arm of the X chromosome (Xq28). In individuals with normal color vision, the locus was proposed to consist of a single red pigment gene upstream of one or more copies of green pigment genes. The presence of a single red pigment gene in the array was confirmed by demonstration of only one retinal mRNA transcript coding for the red opsin. In individuals with multiple green pigment genes, it is unknown whether all genes are expressed. We analyzed the sequence of red- and green-specific mRNA from retinas of individuals with multiple green pigment genes in comparison with the corresponding genomic DNA sequences. The data showed that only a single green pigment gene is expressed. We therefore suggest that a locus control-like element, already known to be located 3.8 kilobases upstream of the transcription initiation site of the red pigment gene, allows transcription of only a single copy of the green pigment genes, probably the most proximal copy. This finding provides an explanation for the not-infrequent presence of 5' green-red hybrid genes in individuals with normal color vision. Such hybrid genes are usually associated with defective color vision. We suggest that 5' green-red hybrid genes produce defective color vision only when their position in the gene array allows expression in the retinal cone cells.
人类的红色和绿色视色素由X染色体长臂（Xq28）上的基因决定。对于具有正常色觉的个体，该基因座被认为由位于一个或多个绿色色素基因上游的单个红色色素基因组成。通过仅展示一个编码红色视蛋白的视网膜mRNA转录本，证实了阵列中存在单个红色色素基因。在具有多个绿色色素基因的个体中，尚不清楚所有基因是否都表达。我们分析了具有多个绿色色素基因的个体视网膜中红色和绿色特异性mRNA的序列，并与相应的基因组DNA序列进行了比较。数据显示只有一个绿色色素基因表达。因此，我们认为一个已知位于红色色素基因转录起始位点上游3.8千碱基处的类似基因座控制元件，使得只有一个绿色色素基因拷贝能够转录，可能是最靠近近端的拷贝。这一发现解释了在具有正常色觉的个体中5'端绿-红杂交基因为何并不罕见。此类杂交基因通常与色觉缺陷相关。我们认为，只有当5'端绿-红杂交基因在基因阵列中的位置允许其在视网膜锥细胞中表达时，才会导致色觉缺陷。
