Toda M, Hirama T, Takeshita S, Yamagishi H
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Immunol Lett. 1989 Jun 15;21(4):311-6. doi: 10.1016/0165-2478(89)90025-4.
We have isolated circular DNAs from splenocytes of euthymic and athymic mice, and prepared the DNA libraries of 1.5 X 10(6) clones. Hundreds of clones homologous to immunoglobulin (Ig) heavy chain segments (DSP2 and DQ52-JH) or light chain segments (J kappa and J lambda) have been identified. Southern hybridization predicted that three of 12 euthymic mouse clones homologous to DQ52-JH and four of 10 athymic mouse clones homologous to DSP2 contained reciprocal recombination products of D-J joining. Some of these clones were characterized by sequencing: two clones contained the precise excision product of the recombination of a DSP2 segment with either JH2 or JH3 segment; two clones showed imprecise ligation of the DSP2-JH2 coding joint and precise ligation of the DFL16.1-JH3 reciprocal joint in the same molecule. They seem to represent a replacement of the pre-existing DSP2-JH2 rearrangement by joining an upstream DFL16 segment to a downstream JH3 segment. The presence in extrachromosomal DNA of a reciprocal recombination product of DH-JH joining is consistent with the view that immunoglobulin genes, like T cell receptor (TCR) genes, can be rearranged in B cell lineage by the looping-out and excision of chromosomal DNA.
我们从正常胸腺小鼠和无胸腺小鼠的脾细胞中分离出环状DNA，并构建了包含1.5×10⁶个克隆的DNA文库。已鉴定出数百个与免疫球蛋白（Ig）重链片段（DSP2和DQ52-JH）或轻链片段（Jκ和Jλ）同源的克隆。Southern杂交预测，12个与DQ52-JH同源的正常胸腺小鼠克隆中有3个，以及10个与DSP2同源的无胸腺小鼠克隆中有4个包含D-J连接的相互重组产物。其中一些克隆通过测序进行了表征：两个克隆包含DSP2片段与JH2或JH3片段重组的精确切除产物；两个克隆显示同一分子中DSP2-JH2编码接头的不精确连接以及DFL16.1-JH3相互接头的精确连接。它们似乎代表了通过将上游DFL16片段与下游JH3片段连接来取代预先存在的DSP2-JH2重排。DH-JH连接的相互重组产物存在于染色体外DNA中，这与免疫球蛋白基因（如T细胞受体（TCR）基因）可通过染色体DNA的环出和切除在B细胞谱系中重排的观点一致。
