Hesse J E, Lieber M R, Mizuuchi K, Gellert M
Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Genes Dev. 1989 Jul;3(7):1053-61. doi: 10.1101/gad.3.7.1053.
Two conserved DNA sequences serve as joining signals in the assembly of immunoglobulins and T-cell receptors from V-, (D)-, and J-coding segments during lymphoid differentiation. We have examined V(D)J recombination as a function of joining signal sequence. Plasmid substrates with mutations in one or both of the heptamer-spacer-nonamer sequences were tested for recombination in a pre-B-cell line active in V(D)J recombination. No signal variant recombines more efficiently than the consensus forms of the joining signals. We find the heptamer sequence to be the most important; specifically, the three bases closest to the recombination crossover site are critical. The nonamer is not as rigidly defined, and it is not important to maintain the five consecutive As that distinguish the consensus nonamer sequence. Both types of signals display very similar sequence requirements and have in common an intolerance for changes in spacer length greater than 1 bp. Although the two signal types share sequence motifs, we find no evidence of a role in recombination for homology between the signals, suggesting that they serve primarily as protein recognition and binding sites.
在淋巴细胞分化过程中，两个保守的DNA序列在免疫球蛋白和T细胞受体由V-、（D）-和J编码片段组装时作为连接信号。我们已将V（D）J重组作为连接信号序列的一个函数进行了研究。对七聚体-间隔区-九聚体序列中一个或两个发生突变的质粒底物，在一个具有活性的V（D）J重组前B细胞系中进行重组测试。没有信号变体比连接信号的共有形式重组效率更高。我们发现七聚体序列最为重要；具体而言，最接近重组交叉位点的三个碱基至关重要。九聚体的定义没有那么严格，维持区分共有九聚体序列的五个连续A并不重要。两种类型的信号都显示出非常相似的序列要求，并且共同的特点是对间隔区长度大于1 bp的变化不耐受。虽然两种信号类型共享序列基序，但我们没有发现信号之间的同源性在重组中起作用的证据，这表明它们主要作为蛋白质识别和结合位点。
