Kim S, Davis M, Sinn E, Patten P, Hood L
Division of Biology, California Institute of Technology, Pasadena 91125.
Cell. 1981 Dec;27(3 Pt 2):573-81. doi: 10.1016/0092-8674(81)90399-8.
The immune response to phosphorylcholine in BALB/c mice has been well characterized. Amino acid sequence analyses of heavy-chain variable (VH) regions from 19 myeloma and hybridoma immunoglobulins binding phosphorylcholine show that 10 are identical (the prototype T15 VH sequence) and 9 are distinct variants differing by one to eight residues. A T15 VH DNA probe was used to isolate four closely related members of the T15 VH gene family, including one encoding the T15 VH sequence, from a sperm genomic library. A comparison of the protein and germline VH sequences suggested that most of the immune response to phosphorylcholine is derived from the T15 germline VH gene segment. The variant heavy chains from the M167 and M603 alpha immunoglobulins differ in their VH protein sequences from T15 by eight and three residues, respectively. We analyzed the somatic variability in and around the coding regions of these two variant VH genes by comparing them with the corresponding regions of the appropriate germline gene segments. The somatic variation has three properties: it is extensive and is found in flanking as well as coding sequences (for example, at least 44 substitutions for the M167 sequence and 10 substitutions for the M603 sequence); in the coding regions, it includes many silent as well as replacement substitutions; and it is focal in nature and centered around the rearranged VH genes. Although the mutations extend into the neighboring upstream and downstream flanking sequences, sequences approximately 5 kb upstream and downstream from the VH genes show no substitutions. Moreover, the associated heavy-chain constant genes (C alpha) from both variant alpha genes are unaltered, indicating that a closely linked and coexpressed gene is unmutated. We conclude that this somatic variation is generated by a special hypermutational mechanism highly localized in its site of execution and highly restricted in its time of operation during B-cell development.
对BALB/c小鼠中磷酰胆碱的免疫反应已得到充分表征。对19种结合磷酰胆碱的骨髓瘤和杂交瘤免疫球蛋白的重链可变（VH）区进行氨基酸序列分析表明，其中10种是相同的（原型T15 VH序列），9种是不同的变体，相差1至8个残基。使用T15 VH DNA探针从精子基因组文库中分离出T15 VH基因家族的四个密切相关成员，包括一个编码T15 VH序列的成员。蛋白质和种系VH序列的比较表明，对磷酰胆碱的大多数免疫反应源自T15种系VH基因片段。来自M167和M603α免疫球蛋白的变体重链在VH蛋白序列上与T15分别相差8个和3个残基。我们通过将这两个变体VH基因的编码区及其周围区域与相应种系基因片段的相应区域进行比较，分析了它们的体细胞变异性。体细胞变异具有三个特性：它是广泛的，存在于侧翼序列和编码序列中（例如，M167序列至少有44个替换，M603序列有10个替换）；在编码区，它包括许多沉默替换和替换替换；并且它本质上是局部的，以重排的VH基因为中心。尽管突变延伸到相邻的上游和下游侧翼序列，但VH基因上游和下游约5 kb的序列没有替换。此外，来自两个变体α基因的相关重链恒定基因（Cα）未改变，表明一个紧密连锁并共表达的基因未发生突变。我们得出结论，这种体细胞变异是由一种特殊的高突变机制产生的，该机制在其执行位点高度局部化，在B细胞发育过程中的作用时间高度受限。
