Proteome-scale tagging and functional screening in mammalian cells by ORFtag [frame_specific_screen]

The systematic determination of protein function is a key goal of modern biology, but remains challenging with current approaches. Here, we present ORFtag, a versatile, cost-effective and highly efficient method for the massively parallel tagging and functional interrogation of proteins at proteome scale. ORFtag utilizes retroviral vectors bearing a promoter, peptide tag and splice donor to generate fusions between the tag and endogenous ORFs. We demonstrate the utility of ORFtag through functional screens for transcriptional activators, repressors and post-transcriptional regulators in mouse embryonic stem cells. Each screen finds known and novel regulators, including long ORFs inaccessible by other methods, revealing that Zfp574 is a highly selective transcriptional activator and that oncogenic fusions often function as transactivators. Activator screen was performed with frame +1, frame+2 and frame+3 ORFtag cassettes separately