Abstract
We have used purified mouse immunoglobulin light chain mRNA and synthetic DNA which is complementary to it to assess the reiteration frequency of gene sequences corresponding to the κ constant region of the mouse immunoglobulin light chain. These studies indicate that the constant region sequence is represented only two to three times per haploid mouse genome, a finding that rules out a simple stringent germ line mechanism which would require the constant region sequence to be represented hundreds if not thousands of times. Hybridization studies involving 125I-labeled myeloma light chain mRNA yield interesting results which may eventually permit us to distinguish between the remaining somatic mutation and recombinational germ line hypotheses. These results reveal a major component of relatively unique frequency and a minor component with a reiteration frequency of approximately 30 to 50 copies per haploid genome. As discussed, these results do not permit us to distinguish unambiguously between a germ line model and a type of somatic mutation model that permits germ line genes corresponding to each κ subgroup. The results do, however, clearly rule out the existence of thousands of variable region sequences so closely related to the MOPC-41 V-region as to permit extensive stable cross-hybridization.
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