Evidence for noncontiguous variable and constant region genes in both germ line and myeloma DNA.

A study has been made of the hybridization of mouse light chain cDNA to restriction enzyme digests of DNA. DNA was digested with B. st (specificity GGATCC) and fractionated on preparative agarose gels for hybridization analysis. Experiments with liver or kidney DNA yielded two peaks of hybridization with V+C cDNA corresponding to the C_κ gene and to the germ line V gene homologous to the MOPC21 V gene. Since there is no site for digestion by B. st within the MOPC21 V or C genes, this result shows that the germ line DNA carries separately the V²¹ and C_κ genes.The hybridization profiles of two different myeloma DNAs (MOPC21 and AdjPC5) differed from those of the germ line DNA. In both myelomas, only one hybridization peak was observed and no peaks corresponding to the germ line pattern were seen. The new pattern of hybridization implies that the events involved in maturation of antibody-producing cells includes rearrangement of the V and C genes.To study whether this proposed rearrangement of DNA results in contiguous V and C genes in producing cells, discrete V+C cDNA size classes (prepared with MOPC21 mRNA) were hybridized to both unfractionated restriction digested MOPC21 DNA and to the partially purified L chain gene of MOPC21 DNA. The length of the cDNA rendered resistant to single-strand-specific S₁ nuclease was determined. In no case was the full length of V+C cDNA protected from nuclease; instead, a fragment of about 290 bases (C region length) plus smaller fragments were generated. These results indicate that the rearrangement of L chain genes, which seems to occur in myeloma cells, may well not produce contiguous V and C genes in the DNA.