Screening of PCRP transcription factor antibodies in biochemical assays
Antibodies offer a powerful means to interrogate specific proteins in a complex milieu, and where epitope tagging is impractical. However, antibody reliability is problematic. The Protein Capture Reagents Program (PCRP) has generated over a thousand renewable monoclonal antibodies against presumptive chromatin proteins in an effort to improve reliability. However, these reagents have not been widely field tested.  We therefore screened them in a variety of chromatin-based assays. 887 unique antibodies against 681 unique chromatin targets were assayed by ChIP-exo. A subset was further tested in ChIP-seq, CUT&RUN, STORM super-resolution microscopy, immunoblots, and PBM protein-DNA interaction assays. At least 5% of the tested antibodies were clearly validated by the most stringent of criteria. However, many others produced data that was distinctly different from background, but whose validity was ambiguous. We demonstrate and discuss the metrics and limitation to antibody validation in chromatin-based assays. Overall design: Large scale screen of PCRP antibodies with ChIP-exo