When IPing my FLAG-tagged protein for ChIP I have used rabbit anti-FLAG and mouse anti-FLAG (both from Sigma) The rabbit anti-FLAG is far superior in our hands in regard to enrichment of DNA bound, has anyone else made this comparison? Thanks.
Sigma's M1 or M2 sometimes lose binding activity to Flag tag depends on its positiion in recombinant protein or buffer conditions. rabbbit anti-flag pAb is a good choice.
I have very different results in immunocytochemistry with flag-rabbit F2555 and flag-mouse F1804 antibodies. The antibodies from mouse are much better!