I am attempting to co-immunoprecipitate a FLAG tagged protein with a myc tagged protein. I am puuling down the FLAG protein and probing for the myc one. My control is simply adding no Ab to one equivalent sample. My problem is the myc tagged protein is being pulled down even in my no Ab control. I use protein A beads and that is what the myc seems to be sticking to. I have tried many different buffers to incubate my IPs in as well as many different wash buffers for my beads. It still seems to stick! Does anyone have any advice and/or ideas?