Sequence diversity within a subgroup of mouse immunoglobulin kappa chains controlled by the IgK-Ef2 locus.

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Abstract
A chromosome 6 locus, IgK-Ef2, controls a pair of prominent bands in normal mouse L chain isoelectric focusing profiles. Screening of myeloma L chains derived from BALB/c mice (an IgK-Ef2a strain) led to the identification of 7 L chains cofocusing with the polymorphic bands controlled by IgK-Ef2. Complete sequencing of the variable (V) regions of 4 of the L chains indicates that they are all members of the same subgroup. (Vk-1A) and they differ from one another by 1-3 substitutions. One of the proteins differs from the prototype V-region sequence only in the deletion of a single residue at position 95 immediately preceding the J (joining) region. The other 2 differ from the prototype V region by 3 (2 framework [fr], 1 complementarity-determining [cdr]) and 1 (fr) residues, respectively. Complete V-region sequences of 2 closely related L chains derived from NZB mice (an IgK-Ef2b strain) indicate the NZB proteins are derived from a distinct Vk gene (Vk-1B), differing by 4 substitutions from the Vk-1A sequence. The IgK-EF2 polymorphism may be a result of, at least in part the loss of the gene(s) coding for the VK-1A subgroup IgK-Ef2b strains of mice. The nature of the sequence diversity found in the Vk-1A subgroup indicates that either it is coded by a repeated series of virtually identical genes or that somatic mutation of a single Vk-1A gene may give rise to substitutions in framework and cdr regions.