[RNAi and the formation of heterochromatin in Schizosaccharomyces pombe.]

International audienceIn the fission yeast Schizosaccharomyces pombe, formation of pericentromeric heterochromatin involves RNA interference (RNAi). Recent data indicate that two RNAi complexes, RITS (RNA-induced transcriptional silencing complex) and RDRC (RNA-directed RNA polymerase complex), their respective enzymatic activity, and RNA polymerase II are essential for RNAi-mediated heterochromatin formation. At the site where heterochromatin formation takes place, RNA polymerase II synthesizes an RNA that would serve as an RNA platform to recruit in a siRNA-dependent manner RITS and RDRC, and thereby initiate heterochromatin assembly. Once recruited, RITS and RDRC seem to also contribute to the processing of the RNA platform. Therefore, RNAi-driven heterochromatin assembly appears to take place through a dynamic process of RNA synthesis, RNA-dependant recruitment of RNAi complexes and RNA degradation that all occur in cis. Chez la levure Schizosaccharomyces pombe, l'assemblage d'h?rochromatine p?centrom?que implique l'interf?nce par l'ARN (iARN). Des donn? r?ntes indiquent que deux complexes de l'iARN, RITS ("RNA-induced transcriptional silencing complex") et RDRC ("RNA-directed RNA polymerase complex"), leur activit?nzymatique respective, ainsi que l'ARN polym?se II sont au coeur du processus de formation d'h?rochromatine guid?ar l'iARN. Au niveau de la r?on ?h?rochromatiniser", l'ARN polym?se II synth?se un ARN, qui servirait de plate-forme pour recruter RITS et RDRC ?a chromatine, et initier la formation d'h?rochromatine. Une fois recrut? RITS et RDRC semblent ?lement participer activement ?a d?adation de l'ARN plate-forme. Ainsi, l'assemblage d'h?rochromatine guid?ar l'iARN mettrait en jeu en cis un processus dynamique de synth? d'ARN, de recrutement ARN-d?ndant de complexes de l'iARN, et de d?adation d'ARN