¹INSERM U384, 28 place Henri Dunant, 63000 Clermont-Ferrand, France

Correspondence: C Vaury, INSERM U384, 28 place Henri Dunant, 63000 Clermont-Ferrand, France. E-mail: Chantal.VAURY@inserm.u-clermont1.fr

Received 20 July 2005; Accepted 17 November 2005; Published online 21 December 2005.

Abstract

RNA silencing is a form of nucleic-acid-based immunity, targeting viruses and genomic repeated sequences. First documented in plants and invertebrate animals, this host defence has recently been identified in mammals. RNAi is viewed as a conserved ancient mechanism protecting genomes from nucleic acid invaders. However, these tamed sequences are known to occasionally escape this host surveillance and invade the genome of their host. This response is consistent with the overall idea that parasitic sequences compete with cells to systematically counter host defences. Using examples taken from the current literature, we illustrate the dynamic move–countermove game played between these two protagonists, the host cell and its parasitic sequences, and discuss the consequences of this game on genome stability.