Structure and expression of a human subgroup II immunoglobulin kappa gene

Genetic studies of four highly homologous rheumatoid factor-associated Vk genes in rheumatoid arthritis patients and normal individuals

Rheumatoid factors (RFs) are autoantibodies directed against IgG molecules. They are present in increased quantity in most patients with rheumatoid arthritis (RA), and are implicated in tissue damage in this disease. Paradoxically, recent studies of RFs have revealed that these autoantibodies are likely a physiological component of the immune system, and may play a role in the development and function of the B cell repertoire. Previously, we found that a significant fraction of RA patients express RF bearing the 6B6.6 cross-reactive idiotype, which is a phenotypic marker of the Humkv328-like genes. In order to elucidate the possible genetic factors that may contribute to the abnormal production of RFs in RA patients, we studied restriction fragment length polymorphisms (RFLP) of four highly homologous RF-related kappa light chain variable region (Vk) genes (i.e. Humkv328, Humkv328h2, Humkv328h5 and Humkv329) in RA patients and normal controls. The results show that kv328, kv328h2 and kv329 are likely to be alleles of the kv328 locus, while kv328h5 is a highly homologous Vk gene residing in a separate locus; and that deletion in one copy of either the kv328 or the kv328h5 loci, but not both loci, occurs in several individuals. However, the frequencies of various RFLP patterns of these two Vk gene loci are similar in patients and normals.

The human VK locus. Characterization of a duplicated region encoding 28 different immunoglobulin genes

Two large regions of the human multigene family coding for the variable parts of the immunoglobulin light chains of the K type (VK) have been characterized on cosmid clones. The two germline regions, called Aa and Ab, span together 250,000 base-pairs and comprise 28 different VK gene segments, nine of which have been sequenced. There is a preponderance of VKII genes but genes belonging to subgroups I and III, and genes that cannot be easily assigned to one of the known subgroups, are interspersed within the VKII gene clusters. A number of pseudogenes have been identified. Within the Aa and Ab regions, all gene segments are organized in the same transcriptional orientation. The regions Aa and Ab, whose restriction maps are highly homologous, were shown not to be allelic structures; they must have arisen by a duplication event. Taken together with previous results, one can conclude that the major part of the VK locus exists in duplicated form. One individual has been found who has only one copy of some of the duplicated regions. By chromosomal walking, the A regions could be linked to the O regions, an analysis of which has been reported. The A regions contribute about one-third of the VK genes so far identified.

Accurate 5' splice-site selection in mouse kappa immunoglobulin light chain premessenger RNAs is not cell-type-specific

In mature mouse B lymphocytes, immunoglobulin kappa light chain transcripts contain an intervening sequence separating the recombined variable (V) plus joining (J) exon from the distant constant (C) exon. After V-J recombination, this intervening sequence can include as many as three unused but very similar J-region 5' splice sites. Each of these sites is potentially functional if the gene is appropriately recombined. It is unclear how the splicing machinery distinguishes among these 5' splice sites, always choosing the most upstream site. We used synthetic transcripts of kappa gene sequences containing J3 and J4 in both the germ-line and the recombined configurations to study the pattern of 5' splice-site selection in vitro. We find that both HeLa cell and lymphocyte nuclear extracts fail to discriminate between the J3- and J4-region 5' splice sites. In contrast, after transfection into HeLa cells, similar kappa light chain transcripts are spliced correctly at the most upstream 5' splice site--that which is used in kappa-producing cells. We conclude that accurate 5' splice-site selection in the mouse kappa light chain is neither cell-type- nor species-specific. Potential mechanisms for this controlling step in gene expression are discussed.