Williams C B, Blankenhorn E P, Byrd K E, Levinson G, Gutman G A
Department of Microbiology and Molecular Genetics, California College of Medicine, University of California, Irvine 92717.
J Immunol. 1991 Jun 15;146(12):4406-13.
We have characterized four overlapping genomic clones containing the DA rat TCR C beta complex, which span a total of 23 kb and bear two closely related complexes of gene segments. The D beta 1-J beta 1-C beta 1 and the D beta 2-J beta 2-C beta 2 complexes each contain a single diversity segment, six joining segments and four exons that encode the C region. All gene segments appear to be functional except J beta 2.5, which has a 5-bp frame-shifting deletion. This organizational pattern is identical to that of the mouse, and the homologous rat and mouse coding regions share about 92% nucleotide sequence identity. Our sequence comparisons indicate that a localized gene correction event has homogenized the sequences of the first exons of C beta 1 and C beta 2 in the evolutionary time since rats and mice became separate species. We have identified three repetitive elements, each flanked by short direct repeats, present in the region "brain-specific" identifier (ID) sequences, another is a truncated member of the LINE I class of repetitive elements, and the third is a member of the Alu type 2 family. The insertion of at least two, and probably all, of these elements has occurred since the time of rat/mouse divergence. We have identified a substantial number of "cryptic" rearrangement signals (heptamer/nonamer) in the C beta locus, which match the consensus sequence as well or better than authentic signals, and may represent sites of nonfunctional rearrangements.
我们已经鉴定出四个重叠的基因组克隆，它们包含DA大鼠TCR Cβ复合体，这些克隆总共跨越23 kb，并带有两个紧密相关的基因片段复合体。Dβ1-Jβ1-Cβ1和Dβ2-Jβ2-Cβ2复合体各自包含一个单一的多样性片段、六个连接片段和四个编码C区域的外显子。除Jβ2.5有一个5 bp的移码缺失外，所有基因片段似乎都具有功能。这种组织模式与小鼠的相同，并且大鼠和小鼠的同源编码区域具有约92%的核苷酸序列同一性。我们的序列比较表明，自大鼠和小鼠成为不同物种以来的进化时间里，一个局部基因校正事件使Cβ1和Cβ2第一个外显子的序列同质化。我们在“脑特异性”标识符（ID）序列区域鉴定出三个重复元件，每个元件两侧都有短的直接重复序列，另一个是LINE I类重复元件的截短成员，第三个是Alu 2型家族的成员。这些元件中至少两个，可能是所有元件的插入都发生在大鼠/小鼠分化之后。我们在Cβ基因座中鉴定出大量“隐蔽”的重排信号（七聚体/九聚体），它们与共有序列匹配得一样好或更好，可能代表无功能重排的位点。
