Effects of siId1 and siId3 on LMP1-mediated decrease of p27. Rat-1 cells were transfected with negative control siRNA (Cy3), siId1, siId3, or siId1 and siId3 and transduced with LMP1-expressing retrovirus, HSCG-LMP1. Expression of Id1 and p27 was determined by immunoblotting (panel A). Expression of Id1 and p27 was quantitated relative to actin expression (numbers below Id1 blot in panel A and black and white bars, respectively, in panel B) using ImageJ densitometry software.