LIMITED FUNCTIONAL DIVERSITY IN KAPPA-LIGHT-CHAINS - JUNCTIONAL SEQUENCES FROM CD43(-CELL PROGENITORS RESEMBLE THOSE FROM PERIPHERAL B-CELLS()B220(+) EARLY B)

Among all adult T and B cell Ag receptor chains, only Ig light chains lack N regions. It is thought that this is due to the fact that light chain genes rearrange after heavy chain genes, and that terminal deoxy nucleotidyl transferase, the enzyme that adds N regions, is no longer expressed at that stage. However, this concept has been challenged rec ently by the demonstration that 3 to 10% of B cell precursors (CD43(+) B220(+)) appear to rearrange their light chains at approximately the s ame time as they undergo V-H-->DJ rearrangements. To examine N region addition in B cell precursors undergoing early kappa-chain rearrangeme nt, we PCR amplified rearranged V(kappa)21 genes from the CD43(+)B220( +) bone marrow cells and compared them to sequences obtained from whol e bone marrow and spleen. Unexpectedly, all three populations showed s imilar to 10% N region containing junctions, most consisting of only o ne N nucleotide. Thus, even the B cell precursors that rearrange light chains at this early stage of development lack much N region diversit y. Twelve percent of the sequences unambiguously contained P regions, which were from 1 to 5 nucleotides in length. All but 2 of the 41 prod uctive rearrangements had the commonly observed CDR3 length of nine am ino acids. Many (71%) of the sequences were out of frame. CDR3 length was very restricted in nonproductive rearrangements too, and deletion of nucleotides from V-kappa and J(kappa) gene segments was limited. Th us, even at the level of nonproductive rearrangements, junctional dive rsity is minimal for kappa-chains.