On a Regulatory Gene Controlling the Expression of the Murine ~1 Light Chain*

The ~.11 light chain is encoded by a single germ-line vx~ and cx~ gene. Upon committment, the vx~ gene is translocated in cis to a transcription unit which includes the ca: gene separated from vxa by a nontranslated stretch of some 1,250 nucleotides (intron) (1). This unit is then transcribed as the high molecular weight nuclear RNA (HnRHA) which must be processed by excision of the intron to yield the polysomebound mRNA in which the coding of vxaand cxamust be contiguous (2, 3). The vx~ germ-line gene complemented with a set of closely-related heavy chain variable region (vn) germ-line genes (referred to as v~,~; a)) encodes the antia(1,3) dextran specificity of high responder strains of mice. The role of the v"~l~ 'a~ genes in the anti-a(1,3) response has been extensively studied (4). Here we deal with the genetics of expression of the ~1 light chain, both in normal immunoglobulin and in the antibody to a(1,3)dextran. This is the first example we have of a regulatory gene linked to the light chain locus which controls specific dominant responsiveness.