Rhodes D A, Stammers M, Malcherek G, Beck S, Trowsdale J
Department of Immunology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom.
Genomics. 2001 Feb 1;71(3):351-62. doi: 10.1006/geno.2000.6406.
We sequenced the 170-kb cluster of BTN genes in the extended major histocompatibility complex region, 4 Mb telomeric of human leukocyte antigen class I genes, at 6p22.1. The cluster consists of seven genes belonging to the expanding B7/butyrophilin-like group, a subset of the immunoglobulin gene superfamily. The main complex is composed of six genes, from two subfamilies, BTN2 and BTN3, arranged in pairs. This alternating pattern must have evolved by duplications of an original block of two genes, one from each subfamily. The sequences from the two subfamilies share approximately 50% amino acid identity. By analysis of repeat elements within each block, these duplications may be dated to approximately 100 million years ago, at about the time of the branching of the Rodentia and Primate lineages. The single BTN1A1 (butyrophilin) gene was positioned approximately 25 kb centromeric to the cluster. Each gene covers approximately 12 kb and consists of seven (BTN2 subfamily) or nine (BTN3 subfamily) coding exons. The predicted leader sequence, immunoglobulin-like IgV (variable)/IgC (constant) ectodomains, and the predicted transmembrane domain are encoded on separate exons and are separated from a B30.2 domain by a variable number of very short exons, 21 and 27 nucleotides in length. BTN transcripts were detected in all tissues examined. Alternative splicing, involving particularly the carboxyl-terminal B30.2 domain, was a notable feature. Most transcripts of BTN2 subfamily genes contained this domain, whereas BTN3 genes did not. Using immunofluorescence, we showed surface expression of BTN-green fluorescent protein fusions in mammalian cell transfectants.
我们对位于人类白细胞抗原I类基因端粒4 Mb处、6p22.1的扩展主要组织相容性复合体区域内170 kb的BTN基因簇进行了测序。该基因簇由七个属于不断扩展的B7/嗜乳脂蛋白样组的基因组成，是免疫球蛋白基因超家族的一个子集。主要复合体由六个基因组成，来自两个亚家族BTN2和BTN3，成对排列。这种交替模式一定是由两个基因的原始片段重复进化而来的，每个亚家族各有一个。两个亚家族的序列氨基酸同一性约为50%。通过分析每个片段内的重复元件，这些重复可能可追溯到约1亿年前，大约在啮齿动物和灵长类谱系分支的时候。单个BTN1A1（嗜乳脂蛋白）基因位于该基因簇着丝粒方向约25 kb处。每个基因覆盖约12 kb，由七个（BTN2亚家族）或九个（BTN3亚家族）编码外显子组成。预测的前导序列、免疫球蛋白样IgV（可变）/IgC（恒定）胞外结构域和预测的跨膜结构域分别由不同的外显子编码，并通过数量可变的非常短的外显子（长度分别为21和27个核苷酸）与B30.2结构域分开。在所有检测的组织中都检测到了BTN转录本。选择性剪接，特别是涉及羧基末端B30.2结构域的剪接，是一个显著特征。BTN2亚家族基因的大多数转录本都包含该结构域，而BTN3基因则没有。我们利用免疫荧光在哺乳动物细胞转染子中显示了BTN-绿色荧光蛋白融合体的表面表达。
