Multi-condition affinity capture/MS analysis of LAP-tagged human NCBP1, NCBP2, and NCBP3

A 5′, 7-methylguanosine cap is a quintessential feature of RNA polymerase II-transcribed RNAs, and thus a textbook aspect of co-transcriptional pre-mRNA processing. The cap is bound by the cap-binding complex (CBC), canonically consisting of nuclear cap-binding proteins 1 and 2 (NCBP1/2). Recently, NCBP3 has been proposed to form an alternative, non-canonical CBC, together with NCBP1. NCBP3 has also been shown to interact with the canonical CBC along with the protein SRRT (aka ARS2), in a manner that is mutually exclusive with the RNA export factor, PHAX. Taken together, ambiguities and missing information in the bona fide physiological protein-protein associations of NCBP3 persist. In an effort to clarify the compositions of NCBP1-, 2-, and 3-related macromolecular assemblies, including their intersections and differences, we have applied our recently developed interactome screening platform (PMID: 25938370). Here the experimental design and data processing have been modified and updated to identify interactome differences between targets of affinity capture under a wide range of experimental conditions, followed by label-free quantitative mass spectrometry.