Identification of mRNA processing complexes bound to histone H2A.2 3’ untranslated region

Processing of 3’ untranslated region (3’-UTR) of precursor messenger RNAs (pre-mRNA) is a fundamental step in mRNA maturation, where the mRNA transcript is cleaved at a specific site, located downstream the open reading frame of the encoded gene. The position of the cleavage site is determined by cis-acting RNA sequence elements, which are recognized with high specificity by large 3’ end processing multiprotein complexes. Two main categories of metazoan 3’ pre-mRNA processing have been identified so far, describing elaboration of either canonical mRNAs – occurring during all phases of the cell cycle and containing a characteristic Poly-Adenylation Signal (PAS) element – or histone mRNAs – prevalently occurring during the S phase and containing a Histone Downstream Element (HDE). In this work, we isolate both human endogenous canonical and histone 3’ pre-mRNA processing complexes from human nuclear extracts by using a pre-mRNA containing the 3’UTR sequence of replication-dependent histone H2A.2. This H2A.2 pre-mRNA (H2A_4m), containing both an HDE sequence and a PAS element in a native overlaid position, was modified with a 5’ photocleavable biotin tag, and with modification of few bases to allow complex assembly and purification by affinity chromatography on streptavidin-agarose beads, elution by UV irradiation and subsequent mass spectrometric identification of bound 3’ mRNA processing factors.