I am attempting an EMSA analysis with protein extracts from vertebrate muscle tissue and biotin-labeled probes synthesized by a company. Whenever I setup my EMSA I get a shift consisting of a double band in all 3 lanes. Lane one containing just the biotin-labeled probe, Lane two containing biotin-labeled probe + protein extract and lane 3 containing biotin-labeled probe + protein extract + specific competitor. I tried running just the labeled probe with each individual buffer component but there was no shift in any of these. The shift in the 3 lanes are all the same and comparable to the control oligo shift (control DNA+ control protein) that comes with my kit. My question is how is it possible that I get a shift in a lane that contains no protein? I have repeated this several times with the same results. One option is protein contamination but it is not competed away and it seems doubtful that trace amounts of protein would cause a shift anyway. Please help.