Figure: V-D-J recombination

Introduction

Genes for lymphocyte antigen receptors are assembled from variable (V), diversity (D) & joining (J) gene segments. V(D)J recombination is initiated by RAG-1 protein & RAG-2 proteins which introduce DNA double strand breaks between the V, D & J segments & their flanking recombination signal sequences (RSSs). RSSs consist of conserved heptamer & nonamer motifs separated by a nonconserved spacer of 12 or 23 base pairs.

The DNA double strand breaks present two types of DNA end structures:

• hairpin sealed coding ends
• phosphorylated blunt signal ends These ends are independently repaired by the non homologous end joining (NHEJ) pathway to form coding & signal joints respectively.