Zezza D J, Stewart S E, Steiner L A
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
J Immunol. 1992 Dec 15;149(12):3968-77.
Xenopus laevis Ig contain two distinct types of L chains, designated rho or L1 and sigma or L2. We have analyzed Xenopus genomic DNA by Southern blotting with cDNA probes specific for L1 V and C regions. Many fragments hybridized to the V probe, but only one or two fragments hybridized to the C probe. Corresponding C, J, and V gene segments were identified on clones isolated from a genomic library prepared from the same DNA. One clone contains a C gene segment separated from a J gene segment by an intron of 3.4 kb. The J and C gene segments are nearly identical in sequence to cDNA clones analyzed previously. The C segment is somewhat more similar and the J segment considerably more similar in sequence to the corresponding segments of mammalian kappa chains than to those of mammalian lambda chains. Upstream of the J segment is a typical recombination signal sequence with a spacer of 23 bp, as in J kappa. A second clone from the library contains four V gene segments, separated by 2.1 to 3.6 kb. Two of these, V1 and V3, have the expected structural and regulatory features of V genes, and are very similar in sequence to each other and to mammalian V kappa. A third gene segment, V2, resembles V1 and V3 in its coding region and nearby 5'-flanking region, but diverges in sequence 5' to position -95 with loss of the octamer promoter element. The fourth V-like segment is similar to the others at the 3'-end, but upstream of codon 64 bears no resemblance in sequence to any Ig V region. All four V segments have typical recombination signal sequences with 12-bp spacers at their 3'-ends, as in V kappa. Taken together, the data suggest that Xenopus L1 L chain genes are members of the kappa gene family.
非洲爪蟾免疫球蛋白包含两种不同类型的轻链，分别命名为rho或L1以及sigma或L2。我们使用针对L1可变区（V）和恒定区（C）的cDNA探针，通过Southern印迹法分析了非洲爪蟾基因组DNA。许多片段与V探针杂交，但只有一两个片段与C探针杂交。在从同一DNA构建的基因组文库中分离出的克隆上鉴定出了相应的C、J和V基因片段。一个克隆包含一个C基因片段，与一个J基因片段被一个3.4 kb的内含子隔开。J和C基因片段的序列与先前分析的cDNA克隆几乎相同。与哺乳动物lambda链的相应片段相比，C片段与哺乳动物kappa链的相应片段在序列上更为相似，而J片段则更为相似。在J片段上游是一个典型的重组信号序列，间隔为23 bp，如同J kappa。文库中的第二个克隆包含四个V基因片段，间隔为2.1至3.6 kb。其中两个，V1和V3，具有V基因预期的结构和调控特征，并且彼此之间以及与哺乳动物V kappa在序列上非常相似。第三个基因片段V2在其编码区和附近的5'侧翼区与V1和V3相似，但在序列上从5'到-95位发生分歧，八聚体启动子元件缺失。第四个类V片段在3'端与其他片段相似，但在密码子64上游的序列与任何免疫球蛋白V区均无相似之处。所有四个V片段在其3'端都有典型的重组信号序列，间隔为12 bp，如同V kappa。综合来看，这些数据表明非洲爪蟾L1轻链基因是kappa基因家族的成员。
