The main goal of this proposal is to build a comprehensive understanding of a new layer of eukaryotic 3’-end precursor-mRNA processing, with focus on the Cleavage Stimulation Factor (CStF) complex. The project stems from the knowledge that targeting of the 3’-end processing machinery can be synthetically lethal in acute myeloid leukemia (AML) and Ewing’s sarcoma. To elucidate the functional role of the CStF complex, we are adopting an integrative structural biology strategy including the molecular reconstitution of CStF from recombinant sources and the determination of its architecture by cryo-EM single particle analysis. The functional role of the newly characterized interactions will be analyzed with biochemical assays and in cancer cells by transcriptional approaches. Our studies will provide molecular knowledge on novel regulatory mechanisms of 3’-end processing and their implication in cancer biology.