Crystal structure of the 25 kDa subunit of human cleavage factor I sub(m)

• Published in: Nucleic acids research 2008-06, Vol.36 (10), p.3474-3483
• Main Authors: Coseno, Molly, Martin, Georges, Berger, Christopher, Gilmartin, Gregory, Keller, Walter, Doublie, Sylvie
• Format: Article
• Language: English
• ISSN: 0305-1048; 1362-4962

Cleavage factor I sub(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 sub(m) is an oligomer composed of a small 25 kDa subunit (CF I sub(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 sub(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 sub(m)25 in its free and diadenosine tetraphosphate (Ap sub(4)A) bound forms at 1.85 and 1.80 Aa, respectively. CF I sub(m)25 crystallizes as a dimer and presents the classical Nudix fold. Results from crystallographic and biochemical experiments suggest that CF I sub(m)25 makes use of its Nudix fold to bind but not hydrolyze ATP and Ap sub(4)A. The complex and apo protein structures provide insight into the active oligomeric state of CF I sub(m) and suggest a possible role of nucleotide binding in either the polyadenylation and/or cleavage steps of pre-messenger RNA 3'-end processing.