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problem in IP - (Jan/01/2014 )

Hello! When I did the IP, I use protein A sepharose beads. I add a negative control which have noting but the beads. When I boil them in the Laemmli sample buffer for 10min, and did SDS-PAGE and western blot, there are smear bands show from ~30kDa to ~60kDa. I really don't understand what are they!? 

Can anybody help?

Thank you!


if you boiled the beads alone in Laemmli the smear may be the BSA that was used to pre-block the beads.