| We have investigated the molecular basis for immunoglobulin kappa (k) light chain markers, designated I(,B) and Efl('a), which are defined by peptide mapping and isoelectric focusing, respectively. These assays detect unique light (L) chains present among pooled L chains from unimmunized mice of the C58, AKR, RF, and PL strains, but not in other strains tested. Congenic strains of mice (C.C58 and C.AKR) made by crossing C58 and AKR mice with the myeloma-inducible Balb/c strain, were used to induce myelomas which produce these L chains. These k chains defined a unique group of k variable regions called V(,k)Ser.;In the present studies, a complementary DNA clone was made from a C.C58 myeloma that secretes a V(,k)Ser light chain. A V(,k)Ser specific hybridization probe was derived from this clone and was used to analyze a panel of inbred strains for the presence of genomic sequences homologous to V(,k)Ser. Southern hybridization experiments showed that such sequences were represented as a single band in all strains tested. A restriction enzyme fragment length polymorphism was observed, which showed that same strain distribution as the I(,B)-peptide and Efl('a) markers. Recombinant DNA libraries were constructed from C.C58 mice, which express V(,k)Ser-associated polymorphisms, and from Balb/c mice, which do not. V(,k)Ser-related genes were isolated and the nucleotide sequences of coding and flanking regions determined. Comparison of these sequences showed that the V(,k)Ser genes of the two strains were >95% homologous, but that nucleotide differences in critical positions in the coding region result in amino acid replacements which could account for failure of Balb/c to express the I(,B)-peptide and Efl('a) markers. Also, a single base substitution was found in the Balb/c sequence in a highly conserved octanucleotide located about 100bp upstream of the V(,k)Ser gene. This difference could have an adverse effect on expression of the V(,k)Ser gene in Balb/c. |
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