Download MendeleyAn alpha motif at Tas3 C terminus mediates RITS cis spreading and promotes heterochromatic gene silencing.
Li, H., Motamedi, M.R., Yip, C.K., Wang, Z., Walz, T., Patel, D.J., Moazed, D.(2009) Mol Cell 34: 155-167
- PubMed: 19394293
- DOI: https://doi.org/10.1016/j.molcel.2009.02.032
- Primary Citation of Related Structures:
3D1B, 3D1D - PubMed Abstract:
RNA interference (RNAi) plays a pivotal role in the formation of heterochromatin at the fission yeast centromeres. The RNA-induced transcriptional silencing (RITS) complex, composed of heterochromatic small interfering RNAs (siRNAs), the siRNA-binding protein Ago1, the chromodomain protein Chp1, and the Ago1/Chp1-interacting protein Tas3, provides a physical tether between the RNAi and heterochromatin assembly pathways. Here, we report the structural and functional characterization of a C-terminal Tas3 alpha-helical motif (TAM), which self-associates into a helical polymer and is required for cis spreading of RITS in centromeric DNA regions. Site-directed mutations of key residues within the hydrophobic monomer-monomer interface disrupt Tas3-TAM polymeric self-association in vitro and result in loss of gene silencing, spreading of RITS, and a dramatic reduction in centromeric siRNAs in vivo. These results demonstrate that, in addition to the chromodomain of Chp1 and siRNA-loaded Ago1, Tas3 self-association is required for RITS spreading and efficient heterochromatic gene silencing at centromeric repeat regions.
Organizational Affiliation:
Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
