Recombination activating genes-1 and -2 of the rabbit: cloning and characterization of germline and expressed genes.

The recombination activating genes RAG-1 and RAG-2 appear to be necessary components of the machinery needed for the Ig or TCR gene rearrangements that occur in developing B and T lymphocytes. In addition RAG-2 has been implicated in the process of V-gene diversification by somatic gene conversion in the chicken. Because gene conversion may be an important mechanism for V-gene diversification in the rabbit, we cloned the rabbit RAG locus and characterized the coding regions of the genomic RAG-1 and RAG-2. In addition, we sequenced cDNAs encompassing the RAG-2 coding region, part of the RAG-2 5' untranslated region and a 967 bp fragment of cDNA from the RAG-1 coding region. Northern analysis revealed a RAG-1 mRNA of 6.6 kb which is similar in size to the RAG-1 mRNA reported previously for other species, and a major species of RAG-2 mRNA of 4.4 kb, which is larger than that from the mouse (2.2 kb). Analysis of the genomic clones showed that, as in other species, the RAG-1 and RAG-2 genes are oriented so as to be convergently transcribed. The DNA sequence analysis showed that the rabbit RAG-1 coding region is 91, 85 and 72% identical to human, mouse and chicken, respectively. The deduced RAG-1 protein sequence for rabbit is 93, 90 and 78% identical to human, mouse and chicken. Comparison of the rabbit RAG-2 coding region revealed 90, 87 and 71% identity to human, mouse and chicken, respectively, at the nucleotide level, and 91, 90 and 72% at the protein level. Although there is considerable conservation of sequence between species, we obtained evidence for allelic forms of the rabbit RAG locus both by Southern analyses and by sequencing. A remarkable degree of polymorphism was found in our rabbit colonies, particularly in the region 3' of the rabbit RAG-2 coding region. A 5' cDNA probe hybridized with one or more additional fragments that are not detected with the coding region probes, suggesting that the 5' cDNA sequence results from splicing of one or more upstream exons.