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

Abstract

The joining (J) segments of mouse immunoglobulin λ light chain genes, λ2, λ3, and a presumptive λ4, were cloned, and their sequences were determined and compared with that of λ1. Although all the λ 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 λ genes occur in two clusters, 5', J3C3J1C13' and 5'J2C2J4C43', further substantiates a probable evolutionary duplication unit, J(II)C(II)J(I)C(I), with II the precursor of λ3 and λ2 and I the precursor of λI and λ4. From the J4 sequence, we conclude that the λ4 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 λ3 as compared with λ1 in mouse serum.