title: Structural basis for the activation of the C. elegans noncanonical cytoplasmic poly(A)-polymerase GLD-2 by GLD-3.
abstract: The Caenorhabditis elegans germ-line development defective (GLD)-2-GLD-3 complex up-regulates the expression of genes required for meiotic progression. GLD-2-GLD-3 acts by extending the short poly(A) tail of germ-line-specific mRNAs, switching them from a dormant state into a translationally active state. GLD-2 is a cytoplasmic noncanonical poly(A) polymerase that lacks the RNA-binding domain typical of the canonical nuclear poly(A)-polymerase Pap1. The activity of C. elegans GLD-2 in vivo and in vitro depends on its association with the multi-K homology (KH) domain-containing protein, GLD-3, a homolog of Bicaudal-C. We have identified a minimal polyadenylation complex that includes the conserved nucleotidyl-transferase core of GLD-2 and the N-terminal domain of GLD-3, and determined its structure at 2.3-Å resolution. The structure shows that the N-terminal domain of GLD-3 does not fold into the predicted KH domain but wraps around the catalytic domain of GLD-2. The picture that emerges from the structural and biochemical data are that GLD-3 activates GLD-2 both indirectly by stabilizing the enzyme and directly by contributing positively charged residues near the RNA-binding cleft. The RNA-binding cleft of GLD-2 has distinct structural features compared with the poly(A)-polymerases Pap1 and Trf4. Consistently, GLD-2 has distinct biochemical properties: It displays unusual specificity in vitro for single-stranded RNAs with at least one adenosine at the 3' end. GLD-2 thus appears to have evolved specialized nucleotidyl-transferase properties that match the 3' end features of dormant cytoplasmic mRNAs.
authors.affiliation: Department of Structural Cell Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany;
authors.forename: Katharina
authors.initials: K
authors.lastname: Nakel
authors.affiliation: Department of Structural Cell Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany;
authors.forename: Fabien
authors.initials: F
authors.lastname: Bonneau
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany.
authors.forename: Christian R
authors.initials: CR
authors.lastname: Eckmann
authors.affiliation: Department of Structural Cell Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany; conti@biochem.mpg.de.
authors.forename: Elena
authors.initials: E
authors.lastname: Conti
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000201:enzymology*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000201:enzymology*; D008958:Models, Molecular; D000073718:Pancreatitis-Associated Proteins; D011062:Polynucleotide Adenylyltransferase / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; C469731:GLD-3 protein, C elegans; D000073718:Pancreatitis-Associated Proteins; C000612141:REG3A protein, human; D016601:RNA-Binding Proteins; C491056:GLD-2 protein, C elegans; D011062:Polynucleotide Adenylyltransferase
keywords: cytoplasmic poly(A)-polymerase; cytoplasmic polyadenylation; germ-line maturation; noncanonical poly(A)-polymerase; posttranscriptional regulation