title: The C-terminal nsP1a protein of human astrovirus is a phosphoprotein that interacts with the viral polymerase.
abstract: Human astrovirus nonstructural C-terminal nsP1a protein (nsP1a/4) colocalizes with the endoplasmic reticulum and viral RNA. It has been suggested that nsP1a/4 protein is involved in the RNA replication process in endoplasmic reticulum-derived intracellular membranes. A hypervariable region (HVR) is contained in the nsP1a/4 protein, and different replicative patterns can be distinguished depending on its variability. In the present work, both the astrovirus RNA-dependent RNA polymerase and four types (IV, V, VI, and XII) of nsP1a/4 proteins have been cloned and expressed in the baculovirus system to analyze their interactions. Different isoforms of each of the nsP1a/4 proteins exist: a nonphosphorylated isoform and different phosphorylated isoforms. While the polymerase accumulates as a monomer, the nsP1a/4 proteins accumulate as oligomers. The oligomerization domain of nsP1a/4-V is mapped between residues 176 and 209. For all studied genotypes, oligomers mainly contain the nonphosphorylated isoform. When RNA polymerase is coexpressed with nsP1a/4 proteins, they interact, likely forming heterodimers. The polymerase binding region has been mapped in the nsP1a/4-V protein between residues 88 and 176. Phosphorylated isoforms of nsP1a/4 type VI show a stronger interactive pattern with the polymerase than the nonphosphorylated isoform. This difference is not observed in genotypes IV and V, suggesting a role of the HVR in modulating the interaction of the nsP1a/4 protein with the polymerase through phosphorylation/dephosphorylation of some critical residues.
authors.affiliation: Enteric Virus Laboratory, Department of Microbiology, University of Barcelona, Barcelona, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Fuentes
authors.forename: Susana
authors.initials: S
authors.lastname: Guix
authors.forename: Albert
authors.initials: A
authors.lastname: Bosch
authors.forename: Rosa M
authors.initials: RM
authors.lastname: Pintó
mesh_terms: D016367:Baculoviridae / Q000235:genetics; D003001:Cloning, Molecular; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D001257:Mamastrovirus / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D055503:Protein Multimerization; D017361:Viral Nonstructural Proteins / Q000378:metabolism*
chemical_list: D010750:Phosphoproteins; D017361:Viral Nonstructural Proteins; D012321:DNA-Directed RNA Polymerases