Artemis, a novel guardian of the genome.

B and T lymphocytes recognize foreign antigen through specialized receptors: the immunoglobulins and the T cell receptors, respectively. The highly polymorphic antigen-recognition regions of these receptors are composed of variable (V), diversity (D), and joining (J) gene segments that undergo somatic rearrangement prior to their expression by the V(D)J recombination process. Proper joining of the V, D, and J segments requires the participation of the Rag proteins as well as the non-homologous end-joining (NHEJ) factors. Recently, a novel V(D)J recombination/NHEJ factor, Artemis, has been identified. Mutations in the ARTEMIS gene cause human severe combined immunodeficiency with increased radiosensitivity (RS-SCID), an autosomal recessive disease characterized by the absence of the T and B lymphocytes and by a defect in the V(D)J recombination. This minireview compiles all mutations in the ARTEMIS gene identified so far. Furthermore, phenotypes of RS-SCID patients and links to the particular mutations are described. Biochemical and structural properties of the Artemis proteins are reviewed and integrated into the processes of V(D)J recombination and NHEJ. A genomic caretaker function is assigned to Artemis.