Evolutionary conservation and molecular cloning of the recombinase activating gene 1⁺⁺

A 700-bp fragment of the recombinase activating gene 1 (RAG-1) was cloned from several evolutionarily distant (sandbar shark, paddlefish, goldfish, axolotl and pig) species using PCR. The nucleotide and deduced amino acid sequences revealed a highly conserved region that has remained essentially unaltered during 400 million years of evolution; e.g, shark and human sequences were 75% identical at the nucleic acid level and 87% as protein. The RAG-1 mRNA levels in the shark were analyzed using semi-quantitative PCR to reveal expression patterns contrary to normal mammalian expression. These results establish that the genetic mechisms for Ig gene rearrangement are present in all extant gnathanstomes.