Immunoglobulin Genes: A Test of Somatic Vs. Germ Line Hypothesis by RNA/DNA Hybridization

Abstract

Sequence analysis of immunoglobulin heavy (H) and light (L) chains has revealed a characteristic pattern: the N-terminal 110–120 amino acid residues vary in some positions from one peptide chain to another, whereas the remaining C-terminal part of the sequenee is common to peptide chains belonging to the same subclass (reviewed by Edelman and Gall, 1969). These two portions of immunoglobulin chains have been designated as the variable (V) and constant (C) regions, respectively. There is considerable genetic evidence that each C region is coded for by a single structural gene (reviewed by Baglioni, 1970). By contrast, it has not yet been established whether each V region is coded for by a different structural gene (germ line hypothesis) or a restricted number of V regions are encoded by structural genes, which undergo mutation during somatic differentiation (somatic mutation hypothesis).