Iwasato T, Shimizu A, Honjo T, Yamagishi H
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Cell. 1990 Jul 13;62(1):143-9. doi: 10.1016/0092-8674(90)90248-d.
We have purified extrachromosomal circular DNAs from adult mouse spleen cells, and cloned into a phage vector the BamHl fragments hybridizing with C mu and S gamma 1 probes. We obtained 52 S mu+S gamma 1+ clones by screening 1.4 million phage clones derived from spleen cells stimulated with bacterial lipopolysaccharide and interleukin 4. We have identified the breakpoints of six clones that contain S gamma 1 and S mu sequences fused in the 5' to 3' orientation. All these switch recombination sites were assigned to the central repetitive sequences of the S mu and S gamma 1 regions. Since the common S mu-S gamma 1 sequences at the recombination sites are at most 2 bases long, typical homologous recombination cannot account for their joining. These findings provide direct evidence that mu-gamma 1 class switching can occur by the looping out and excision of chromosomal DNA, with formation of a circle.
我们从成年小鼠脾细胞中纯化了染色体外环状DNA，并将与Cμ和Sγ1探针杂交的BamHl片段克隆到噬菌体载体中。通过筛选140万个源自用细菌脂多糖和白细胞介素4刺激的脾细胞的噬菌体克隆，我们获得了52个Sμ+Sγ1+克隆。我们确定了六个克隆的断点，这些克隆包含以5'至3'方向融合的Sγ1和Sμ序列。所有这些开关重组位点都位于Sμ和Sγ1区域的中央重复序列上。由于重组位点处的常见Sμ-Sγ1序列最长为2个碱基，典型的同源重组无法解释它们的连接。这些发现提供了直接证据，表明μ-γ1类转换可以通过染色体DNA的环出和切除并形成一个环来发生。
