5164 Nucleic Acids Research, 2007, Vol. 35, No. 15 32. Haase,A.D., Jaskiewicz,L., Zhang,H., Laine,S., Sack,R., Gatignol,A. and Filipowicz,W. (2005) TRBP, a regulator of cellular PKR and HIV-1 virus expression, interacts with Dicer and functions in RNA silencing. EMBO Rep., 6, 961–967. 33. Koller,E., Propp,S., Murray,H., Lima,W., Bhat,B., Prakash,T.P., Allerson,C.R., Swayze,E.E., Marcusson,E.G. et al. (2006) Competition for RISC binding predicts in vitro potency of siRNA. N ucleic Acids Res., 34, 4467–4476. 34. Gregory,R.I., Chendrimada,T.P., Cooch,N. and Shiekhattar,R. (2005) Human RISC couples MicroRNA biogenesis and posttranscriptional gene silencing. Cell, 123, 631–640. 35. Nishitsuji,H., Kohara,M., Kannagi,M. and Masuda,T. (2006) Eﬀective suppression of human immunodeﬁciency virus type 1 through a combination of short- or long-hairpin RNAs targeting essential sequences for retroviral integration. J. Virol., 80, 7658–66.