Mouse V lambda x gene sequence generates no junctional diversity and is conserved in mammalian species.

The lambda x, a new mouse Ig lambda L chain, is produced by rearrangement of the V lambda x, J lambda 2, and C lambda 2 gene segments. The V lambda x amino acid sequence is as divergent to other V lambda as to Vk gene sequences. Additionally, its third hypervariable region (CDR3) is four amino acids longer than those of all other variable gene segments of murine L chain. We have cloned and sequenced the germ-line V lambda x gene and found that the unexpected CDR3 length is encoded by the V lambda x gene. Junctional diversity is prevented by a TAA termination codon localized at the V lambda x 3' extremity. Moreover, we show a striking conservation of the V lambda x sequence in various mammalian species. Portions of the V lambda x sequence display more than 70% of nucleotide sequence identity with rabbit and human variable regions. These results suggest that V lambda x predated the divergence of mammalian species.