Caretakers and gatekeepers

Cellular gatekeepers include the proteins that regulate cell cycle progression in response to DNA damage, and the DNA repair pathways function as genomic caretakers. The p53 and ATM (ataxia-telangiectasia-mutated) proteins behave as cellular gatekeepers, whereas the non-homologous end-joining (NHEJ) DNA repair machinery acts as a genomic caretaker. NHEJ factors include Ku70, Ku80 and the DNA-PK enzyme, plus XXRC4 and DNA Ligase IV (Lig4), which function in ligation.

In 6 March Proceedings of the National Academy of Sciences, USA Sekiguchi and colleagues report that mutation of the ATM gene rescues the embryonic lethality and neuronal apoptosis associated with Lig4 deficiency in mice (PNAS 2001, 98:591-596). ATM deficiency failed to relieve defects in lymphocyte development due to the absence of Lig4. These results are similar to observations in Lig4^-/^-p53^-/^- mice. ATM deficiency also increased the genome instability, senescence and growth defects of Lig4-deficient fibroblasts.

Surprisingly, Sekiguchi et al report that deletion of ...