UPDATE: V(D)J Recombination and Transposition: Closer Than Expected

In a recent Perspective, I outlined the similarities among different transposition reactions—the movement of bacterial DNA segments and the replication and integration of certain bacteriophages and of retroviral DNA (1). All are mediated by recombinases of related structure that execute DNA breakage and joining by transesterification reactions. Now, in a report in this week's issue (2) V(D)J recombination, which underlies the ability of the immune system to assemble many different antigen-specific genes from separate gene segments, joins the family of transposition reactions.