Protecting genomic integrity during DNA replication: correlation between Werner's and Bloom's syndrome gene products and the MRE11 complex.

DNA replication is a critical step for cells because of the propensity of replication forks to stall, as a consequence either of endogenous DNA damage or of the propensity of repeated sequences to form tertiary structures, which can impede fork progression. Moreover, as a result of stalled replication fork processing, potentially lethal and recombinogenic double-strand breaks can be formed. Thus cells (in particular human cells) have evolved a sophisticated network to deal with replication fork stall. Recently, WRN and BLM, two helicases mutated in the genetic hereditary conditions Werner and Bloom syndromes, appeared crucial for the correct recovery from replication arrest; however, it seems that other proteins assist them in this role. One of the possible partners is the MRE11 complex, which is found mutated in two other genetic instability syndromes: Nijmegen breakage syndrome and ataxia telangiectasia-like disorder. This strongly supports the idea of a central role of preventing crisis during DNA replication for the maintenance of genomic stability and integrity in human cells.