The extent of rearrangements of immunoglobulin genes was investigated. The deoxyribonucleic acids (DNAs) of four K-chain-producing myelomas (MOPC-167, MOPC-41, MOPC-21, and MOPC-321), one X-chain myeloma (S178), Krebs ascites cells, liver, spleen, and thymus were digested with six different restriction endonucleases (KpnI, EcoRI, PvuII, Xbal, HirtdIII, and BamHI) used alone or in all possible pairs. Following agarose gel electrophoresis and transfer to nitrocellulose filters [Southern, E. M. (1975) J. Mol. Biol. 98, 503], the DNAs were hybridized to one of three phosphorus-32 nick-translated probes: one for the K-chain constant (C) region, one for the MOPC-167 K-chain variable (V) region, and one for both the C and V regions. The probes were derived from a cloned complementary deoxyribonucleic acid from myeloma MOPC-167. It was found that liver, spleen, thymus and Krebs DNAs always produced hybridization band patterns indistinguishable from one another when a given enzyme or enzyme pair was used. One myeloma (MOPC-321) produced these same “germline” bands, but always exhibited other bands as well. The other four myelomas exhibited banding patterns which were not superimposable over the normal tissue pattern. Hybridization banding data obtained after double-enzyme digestion allowed the construction of restriction maps for sequences surrounding the C- and V-region genes in each of the DNAs. V maps for the MOPC-167 sequence were invariant in all DNAs except MOPC-167, indicating an absence of rearrangement in cells which do not express V167. MOPC-167 showed single nongermline V and C maps which overlapped in such a way that the V- and C-containing fragments were about 1 kilobase (kb) apart. The 6 kb mapped at the 5' side of the MOPC-167 V167 gene were identical with the sequence flanking the germline V167 gene. A single map, presumably in a germline configuration, was obtained for the sequences surrounding the C-region gene for the liver, spleen, thymus, and Krebs ascites cells. MOPC-321 had a map which was identical with this germline map, but it had in addition two rearranged C maps. The four other myelomas each gave one to three rearranged C maps, none of which were identical with any other C map. It was concluded that phenotypic “allelic exclusion” in myeloma cells is not necessarily correlated with the maintenance of one normal chromosome. A C-map comparison revealed that most restriction site alterations occur within 10 kb beyond the 5' end of the restriction fragment carrying the C-region gene. Other features emerging from this study were the following. (1) All cells tested have multiple V167-like sequences in identical restriction fragments. (2) S178, a λ myeloma, displays shifted k genes. This correlates with our previous finding that SI78 cells contain a low level of k ribonucleic acid (RNA) [Storb, U., Hager, L„ Wilson, R., & Putnam, D. (1977) Biochemistry 16, 5432]. There must therefore exist transcriptional or posttranscriptional controls in this tumor which limit the accumulation of k mRNA but not λ mRNA. (3) The DNAs of spleen and thymus, organs which contain 87 and 99%, respectively, of cells which produce k RNA [Storb, U. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 2905], showed a germline restriction map for Ck genes, suggesting that the majority of k genes are not rearranged in these cells or that one of the allelic Ck genes is maintained in a germline context. It is not yet known whether the differences between the myeloma cells tested and the nonmalignant lymphoid tissues are due to the polyploidy or to the differentiated plasma cell nature of the myeloma. © 1979, American Chemical Society. All rights reserved.
