Wright C V, Cho K W, Fritz A, Bürglin T R, De Robertis E M
Department of Biological Chemistry, University of California School of Medicine, Los Angeles 90024.
EMBO J. 1987 Dec 20;6(13):4083-94. doi: 10.1002/j.1460-2075.1987.tb02754.x.
A cDNA clone (p52) that contains all the protein-coding region from the maternally expressed XlHbox 2 locus of the frog Xenopus laevis has been isolated and sequenced. A probe containing the exon preceding the homeobox detected transcripts which arise from a splicing event in which the homeobox-containing exon is replaced by another exon lying 5' to it in the genome. Both the homeobox-containing and homeobox-less splicing event occur in the same tissues, with the homeobox-less RNA representing the minority of mRNA from this gene. There may therefore be a function for two types of transcript, and hence protein, from this locus. This phenomenon may not be exclusive to the XlHbox 2 gene of Xenopus, but might occur more generally in other homeobox-containing genes. The protein deduced from the homeobox-containing cDNA is significantly similar to the yeast mating type factor a1 (MAT-a1) gene product. In addition to the previously described homology of the homeodomains, the amino-terminal domains of XlHbox 2 and MAT-a1 are similar to each other; thus essentially all of the MAT-a1 protein corresponds to some part of the XlHbox 2 protein. In the case of XlHbox 2, the protein coded for by the homeoboxless mRNA would contain all of the non-homeobox homology to yeast MAT-a1.
已分离并测序了一个来自非洲爪蟾母源表达的XlHbox 2基因座的cDNA克隆（p52），它包含该基因座所有的蛋白质编码区。一个含有位于同源异型框之前外显子的探针检测到了转录本，这些转录本源于一种剪接事件，在该事件中，含有同源异型框的外显子被基因组中位于其5'端的另一个外显子所取代。含同源异型框和不含同源异型框的剪接事件都发生在相同的组织中，不含同源异型框的RNA占该基因mRNA的少数。因此，该基因座可能存在两种类型转录本，进而存在两种类型蛋白质的功能。这种现象可能并非爪蟾XlHbox 2基因所特有，而是可能更普遍地发生在其他含同源异型框的基因中。从含同源异型框的cDNA推导的蛋白质与酵母交配型因子a1（MAT-a1）基因产物显著相似。除了先前描述的同源异型结构域的同源性外，XlHbox 2和MAT-a1的氨基末端结构域也彼此相似；因此，MAT-a1蛋白基本上全部对应于XlHbox 2蛋白的某些部分。就XlHbox 2而言，由不含同源异型框的mRNA编码的蛋白质将包含与酵母MAT-a1所有非同源异型框的同源部分。
