Inha Heo1 and V. Narry Kim1,*
1School of Biological Sciences and National Creative Research Initiatives Center, Seoul National University, Seoul 151-742, Korea
Every regulator should be regulated, and this holds true for small RNAs and their associated proteins. Knowledge has begun to emerge of the various mechanisms that impose specificity on the expression and function of RNA silencing factors. Recent papers, including one in this issue of Cell (Paroo et al., 2009), now reveal the posttranslational modifications that take part in the regulation of the core RNA silencing factors, Ago, Piwi, and TRBP.