From Proteopediaproteopedia link
Structure of Yeast Poly(A) Polymerase with ATP and oligo(A)
[PAP_YEAST] Polymerase component of the cleavage and polyadenylation factor (CPF) complex, which plays a key role in polyadenylation-dependent pre-mRNA 3'-end formation and cooperates with cleavage factors including the CFIA complex and NAB4/CFIB. 
Publication Abstract from PubMed
We report the 1.8 A structure of yeast poly(A) polymerase (PAP) trapped in complex with ATP and a five residue poly(A) by mutation of the catalytically required aspartic acid 154 to alanine. The enzyme has undergone significant domain movement and reveals a closed conformation with extensive interactions between the substrates and all three polymerase domains. Both substrates and 31 buried water molecules are enclosed within a central cavity that is open at both ends. Four PAP mutants were subjected to detailed kinetic analysis, and studies of the adenylyltransfer (forward), pyrophosphorolysis (reverse), and nucleotidyltransfer reaction utilizing CTP for the mutants are presented. The results support a model in which binding of both poly(A) and the correct nucleotide, MgATP, induces a conformational change, resulting in formation of a stable, closed enzyme state. Thermodynamic considerations of the data are discussed as they pertain to domain closure, substrate specificity, and catalytic strategies utilized by PAP.
Mechanism of poly(A) polymerase: structure of the enzyme-MgATP-RNA ternary complex and kinetic analysis.,Balbo PB, Bohm A Structure. 2007 Sep;15(9):1117-31. PMID:17850751
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.