Co-immunoprecipitation (Co-IP) of miRNP with anti-Ago1 (Abcam, Cambridge, MA, USA) or IgG (Sigma) was performed as previously described (Tan et al, 2009 (link)). RNA co-immunoprecipitated with anti-Ago1 or IgG antibodies was extracted using TRIzol LS (Invitrogen) as described in a previous publication (Cheng et al, 2008 (link)). Total RNA was subjected to DNA digestion as described above.