DNA sequences of the joining regions of mouse lambda light chain immunoglobulin genes

The joining (J) segments of mouse immunoglobulin lambda light chain genes, lambda 2, lambda 3, and a presumptive lambda 4, were cloned, and their sequences were determined and compared with that of lambda 1. Although all the lambda J segments share sequence homology, the J1 and J4 segments and the J2 and J3 segments, respectively, are more homologous. These sequence data, together with the fact that present day lambda genes occur in two clusters, 5' J3C3J1C1 3' and 5' J2C2J4C4 3', further substantiates a probable evolutionary duplication unit, JIICIIJICI, with II the precursor of lambda 3 and lambda 2 and I the precursor of lambda I and lambda 4. From the J4 sequence, we conclude that the lambda 4 gene is most likely nonfunctional (i.e., a pseudogene). The signal nonamer sequence 5' to J3 differs from that of J1 in two consecutive base pairs. This difference could account in part for the lower level of expression of lambda 3 as compared with lambda 1 in mouse serum.