Perhaps one of the most unique horizontal transfer
events to have occurred was from bacteria to vertebrates.
The rearrangement of antibody and T-cell receptors is
indispensable to the vertebrate immune response, and is
conferred by the recombination activating genes I and II
(RAG I and II) (Bernstein et al., 1996) An examination of
one of the most primitive jawed vertebrates, the carnachine
sharks, showed that the sequence of RAG I and RAG II
were most closely related to the integrase family of genes