Résumé
Emerging evidence suggests that RNA interference (RNAi)-related processes act both in the cytoplasm and in the nucleus. However, the process by which the RNAi machinery is transported into the nucleus remains poorly understood. The
Tetrahymena Argonaute protein Twi1p localizes to the nucleus and is crucial for small RNA-directed programmed DNA elimination. In this study, we identify Giw1p, which binds to Twi1p and is required for its nuclear localization. Furthermore, the endoribonuclease (Slicer) activity of Twi1p plays a vital role in the removal of one of the two strands of Twi1p-associated small interfering RNAs (siRNAs), leading to a functionally mature Twi1p-siRNA complex. Slicer activity is also shown to be required for nuclear localization of Twi1p and for its association with Giw1p. These results suggest that Giw1p senses the state of Twi1p-associated siRNAs and selectively transports the mature Twi1p-siRNA complex into the nucleus.
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► siRNA-directed DNA elimination in
Tetrahymena requires Twi1p, an Argonaute protein ► We have uncovered Giw1p as a factor required for macronuclear localization of Twi1p ► Twi1p's slicer activity removes siRNA passenger strand, allowing Giw1p to bind Twi1p ► Twi1p slicer activity and Giw1p are required for the programmed DNA elimination