Toyonaga B, Yoshikai Y, Vadasz V, Chin B, Mak T W
Proc Natl Acad Sci U S A. 1985 Dec;82(24):8624-8. doi: 10.1073/pnas.82.24.8624.
The organization and sequences of the human beta-chain T-cell receptor diversity, joining, and constant region segments are described. The beta chain of the human T-cell receptor, analogous to the mouse counterpart, consists of two distinct constant region genes approximately equal to 10 kilobases apart. The two constant region genes, C beta 1 and C beta 2, are very similar not only in sequence but also in genomic organization. The coding sequences of each of these C beta constant region genes are divided into four exons. The first two exons encode most of the extracellular constant domain. The third exon encodes a major part of the presumed transmembrane portion, and the last exon contains the cytoplasmic coding sequence as well as 3' untranslated sequences. Except for a stretch of approximately equal to 95 highly conserved nucleotides extending 3' of the first exon of the C region genes, little homology can be found between the intron sequences of C beta 1 and C beta 2. A small cluster of joining region (J beta) gene segments is located approximately equal to 5 kilobases upstream of each of these two constant regions. The first cluster, J beta 1, contains six functional J gene segments while the second, J beta 2, contains seven functional J gene segments. In addition, diversity region (D beta) gene segments are located approximately equal to 600 base pairs upstream of each J beta. Recombinational signals containing highly conserved heptamer and nonamer sequences separated by 12 or 23 bases are found adjacent to all of these D beta and J beta gene segments. These signal sequences are thought to be involved in the somatic recombination processes. These results indicate that what appears to be a gene duplication event giving rise to these two distinct regions must have arisen a long time ago in the evolution of this gene locus.
本文描述了人类β链T细胞受体多样性、连接区和恒定区片段的组织及序列。人类T细胞受体的β链与小鼠对应物类似，由两个相距约10千碱基的不同恒定区基因组成。这两个恒定区基因Cβ1和Cβ2不仅在序列上非常相似，在基因组组织上也很相似。每个Cβ恒定区基因的编码序列被分为四个外显子。前两个外显子编码大部分细胞外恒定结构域。第三个外显子编码推测的跨膜部分的主要部分，最后一个外显子包含细胞质编码序列以及3'非翻译序列。除了C区基因第一个外显子3'端延伸约95个高度保守的核苷酸片段外，Cβ1和Cβ2的内含子序列之间几乎没有同源性。一小簇连接区（Jβ）基因片段位于这两个恒定区各自上游约5千碱基处。第一个簇Jβ1包含六个功能性J基因片段，而第二个Jβ2包含七个功能性J基因片段。此外，多样性区（Dβ）基因片段位于每个Jβ上游约600个碱基对处。在所有这些Dβ和Jβ基因片段相邻位置发现了含有由12或23个碱基分隔的高度保守七聚体和九聚体序列的重组信号。这些信号序列被认为参与体细胞重组过程。这些结果表明，导致这两个不同区域出现的基因重复事件一定是在该基因座的进化过程中很久以前发生的。
