Mouse immunoglobulin genes: studies on the reiteration frequency of light-chain genes by hybridisation procedures.

The partially purified immunoglobulin light chain messenger RNA fraction from P3K (MOPC 21) mouse myeloma tissue-culture cells has been employed in hybridisation studies. Fragments of the messenger RNA were generated by alkali hydrolysis. 6-S fragments not containing poly(A) showed the characteristic biphasic hybridisation profile seen with the intact RNA fraction. 12-S and 6-S poly(A)-containing fragments, however, showed single transitions lacking the rapidly hybridising component. Complementary DNA copies of the intact messenger RNA fraction were prepared with RNA-dependent DNA polymerase and the DNA populations fractionated on acrylamide gels. Hybridisation experiments with complementary DNA fractions up to 800 bases in length showed annealing to single (or a few) genes. A rapidly hybridising component (about 200 copies) appears in the cDNA fraction containing the largest transcripts. We conclude that the kappa constant region gene and the MOPC 21 variable region gene are present as one or a few copies in the haploid genome and that the rapidly hybridising component is not due to variable region genes.