double band with anti-Flag but not with anti-HA antibody - (Oct/13/2014 )

Hi everybody, I've got a Flag-tagged RRAS and a HA-tagged RRAS. After a transient transfection, I detected RRAS by western blot with an anti-HA and anti-Flag antibody. With the anti-Flag antibody I detected a double band, one with the correct molecular weight and one with a higher molecular weight. With the HA-antibody I detected a single band. Does anybody have a similar problem? I thought that maybe the double band is because of phosphorylation related to GTP- and GDP-bound RRAS but that would still not explain why I couldn't detect a double band with the anti-HA antibody...

Does anybody have an idea?

Thanks a lot!

How much bigger is the double band? do you have a known positive single band FLAG that you can use to test?