RAG1 gene mutations and residual recombination activity. Sequence alignment of RAG1 protein of different species. Both the arginine (R) at amino acid position 474 and the leucine (L) at 506 are conserved residues. (A) The parents were heterozygous for each of the mutation. (B) Transfection of pDVG93, RAG1 and RAG2 in 3T3 fibroblasts results in an inversion rearrangement of pDVG93, which can be detected by the primers DG89 and DG147. (C) Only the R474C mutation results in residual recombination activity, as assessed by the in vitro recombination assay using pDVG93.