Regulating the regulators: posttranslational modifications of RNA silencing factors.

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.