title: Crystal structure of the 25 kDa subunit of human cleavage factor Im.
abstract: Cleavage factor I(m) is an essential component of the pre-messenger RNA 3'-end processing machinery in higher eukaryotes, participating in both the polyadenylation and cleavage steps. Cleavage factor I(m) is an oligomer composed of a small 25 kDa subunit (CF I(m)25) and a variable larger subunit of either 59, 68 or 72 kDa. The small subunit also interacts with RNA, poly(A) polymerase, and the nuclear poly(A)-binding protein. These protein-protein interactions are thought to be facilitated by the Nudix domain of CF I(m)25, a hydrolase motif with a characteristic alpha/beta/alpha fold and a conserved catalytic sequence or Nudix box. We present here the crystal structures of human CF I(m)25 in its free and diadenosine tetraphosphate (Ap(4)A) bound forms at 1.85 and 1.80 A, respectively. CF I(m)25 crystallizes as a dimer and presents the classical Nudix fold. Results from crystallographic and biochemical experiments suggest that CF I(m)25 makes use of its Nudix fold to bind but not hydrolyze ATP and Ap(4)A. The complex and apo protein structures provide insight into the active oligomeric state of CF I(m) and suggest a possible role of nucleotide binding in either the polyadenylation and/or cleavage steps of pre-messenger RNA 3'-end processing.
authors.affiliation: Department of Microbiology and Department of Molecular Genetics, University of Vermont, Burlington, VT 05405, USA.
authors.forename: Molly
authors.initials: M
authors.lastname: Coseno
authors.forename: Georges
authors.initials: G
authors.lastname: Martin
authors.forename: Christopher
authors.initials: C
authors.lastname: Berger
authors.forename: Gregory
authors.initials: G
authors.lastname: Gilmartin
authors.forename: Walter
authors.initials: W
authors.lastname: Keller
authors.forename: Sylvie
authors.initials: S
authors.lastname: Doublié
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019281:Dimerization; D015226:Dinucleoside Phosphates / Q000737:chemistry; D006801:Humans; D008670:Metals / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D016415:Sequence Alignment; D055672:Static Electricity; D039221:mRNA Cleavage and Polyadenylation Factors / Q000737:chemistry*
chemical_list: D015226:Dinucleoside Phosphates; D008670:Metals; D021122:Protein Subunits; C450562:cleavage factor Im, human; D039221:mRNA Cleavage and Polyadenylation Factors; C020733:diadenosine tetraphosphate