DYRK1A phosphorylates SF3b1 within the TP-domain. A, Phosphorylation of His6-SF3b1304–493 by DYRK1A. – Data from a representative experiment were evaluated by linear regression analysis of the Lineweaver-Burke plot. B, Schematic representation of human SF3b1 and the recombinant fusion proteins used in this study. The carboxyterminal part of SF3b1 consists of 22 nonidentical repeats related to the regulatory subunit A of protein phosphatase 2A (PP2A-like) . Numbers indicate amino acids. TP-rich, region rich in Thr-Pro dipeptides; His, hexahistidine tag.