Western blot analysis of extracts from HeLa cells, transfected with 100 nM SignalSilence ® Control siRNA (Unconjugated) #6568 (-), SignalSilence ® SP1 siRNA I #12104 (+), or SignalSilence ® SP1 siRNA II (+), using SP1 Antibody #5931 (upper) or β-Actin (D6A8) Rabbit mAb #8457 (lower). The SP1 Antibody confirms silencing of SP1 expression, while the β-Actin (D6A8) Rabbit mAb is used as a loading control. The SP1 Antibody cross-reacts with a protein of unknown origin at 55 kDa, which is unaffected by SignalSilence ® SP1 siRNA I #12104 or SignalSilence ® SP1 siRNA II.