Nucleotide sequencing of human and mouse RAG1 cDNA clones encode predicted 119-kD proteins of 1,043 and 1,040 amino acids, respectively, with 90% sequence identity. The RAG1 gene has been conserved between species that carry out the V(D)J recombination, and its pattern of expression correlates exactly with the pattern of expression of V(D)J recombinase activity. Oettinger et al. (1990) gave a corrected length of 6.6 kb for the RAG1 cDNA.

RAG1 is critical for joining in vivo and strongly suggesting that the postcleavage complex is important in end joining. The E423Q mutant was severely defective for both hairpin opening in vitro and coding joint formation in vivo. These data suggested that the hairpin opening activity of the RAG proteins plays an important physiologic role in V(D)J recombination.