Human immunoglobulin variable region genes—DNA sequences of two Vκ genes and a pseudogene

Abstract

The study of immunoglobulin genes at the molecular level can allow us to elucidate the origin of antibody diversity. Investigations of immunoglobulin gene structure in the mouse have shown that light chains are encoded by three gene segments: the C gene encoding the constant region and the V and J genes encoding the variable region. In antibody-producing cells the V and J genes join together to create a complete immunoglobulin gene^1,2. No data are available on the structure of human light chain variable region genes, but the variable regions of over 150 human κ light chain proteins have been sequenced and they comprise four distinct subgroups^3–5. Here we report the complete DNA sequences of three human κ variable region (V_κ) genes isolated from fetal liver DNA. The sequences demonstrate that two non-allelic genes encoding subgroup I proteins have more than 90% nucleotide homology in both coding and non-coding regions. Comparison of these human genes with two complete DNA sequences of mouse V_κ genes^6,7 shows that V_κ gene structure is highly conserved between the two species, which suggests that V_κ genes rearrange during the differentiation of human lymphocytes by a very similar mechanism to that in the mouse^8,9. The sequence of a defective V_κ gene is also described—this gene is unable to code for a functional immunoglobulin due to substitutions, deletions and insertions in its sequence. It is analogous to the pseudogenes¹⁰ of globin^11–13 and Xenopus 5S RNA¹⁴.