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	Biochemistry Jul (2008); 47(26):6859-69
Structure of yeast poly-A- polymerase in complex with a peptide from Fip1, an intrinsically disordered protein-
Meinke G, Ezeokonkwo C, Balbo P, Stafford W, Moore C, Bohm A
Department of Biochemistry, Tufts University, 136 Harrison Avenue, Boston, Massachusetts 02111, USA-
Abstract: In yeast, the mRNA processing enzyme poly-A- polymerase is tethered to the much larger 3'-end processing complex via Fip1, a 36 kDa protein of unknown structure- We report the 2-6 A crystal structure of yeast poly-A- polymerase in complex with a peptide containing residues 80-105 of Fip1- The Fip1 peptide binds to the outside surface of the C-terminal domain of the polymerase- On the basis of this structure, we designed a mutant of the polymerase -V498Y, C485R- that is lethal to yeast- The mutant is unable to bind Fip1 but retains full polymerase activity- Fip1 is found in all eukaryotes and serves to connect poly-A- polymerase to pre-mRNA processing complexes in yeast, plants, and mammals- However, the Fip1 sequence is highly divergent, and residues on both Pap1 and Fip1 at the observed interaction surface are poorly conserved- Herein we demonstrate using analytical ultracentrifugation, circular dichroism, proteolytic studies, and other techniques that, in the absence of Pap1, Fip1 is largely, if not completely, unfolded- We speculate that flexibility may be important for Fip1's function as a molecular scaffold-
[PUBMED: 18537269]