Amino acid sequences of rabbit light chains show considerable evidence of independent assortment of framework (FR) and complementarity-determining (CDR) segments. This suggests that they are coded for by independent genetic units (minigaenes) and that individual light chains are assembled somatically by recombining these units. Identical FR sets with multiple members generally comprise chains with different specificities, whereas identical CDR sets tend to have chains of a single specificity. A J segment, which, by analogy with mouse light chains, is made up of the last two residues of CDR3 plus all of FR4, contained 18 different sets and could contribute to diversity generated by CDR3. The longest segment, FR3, had a very large number of sets. Evidence is presented showing that the number of sets could be substantially reduced by permitting FR3 to be formed by two independently assorting segments comprising residues 57-68 and 69-88.

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