title: Mechanism for template-independent terminal adenylation activity of Qβ replicase.
abstract: The genomic RNA of Qβ virus is replicated by Qβ replicase, a template-dependent RNA polymerase complex. Qβ replicase has an intrinsic template-independent RNA 3'-adenylation activity, which is required for efficient viral RNA amplification in the host cells. However, the mechanism of the template-independent 3'-adenylation of RNAs by Qβ replicase has remained elusive. We determined the structure of a complex that includes Qβ replicase, a template RNA, a growing RNA complementary to the template RNA, and ATP. The structure represents the terminal stage of RNA polymerization and reveals that the shape and size of the nucleotide-binding pocket becomes available for ATP accommodation after the 3'-penultimate template-dependent C-addition. The stacking interaction between the ATP and the neighboring Watson-Crick base pair, between the 5'-G in the template and the 3'-C in the growing RNA, contributes to the nucleotide specificity. Thus, the template for the template-independent 3'-adenylation by Qβ replicase is the RNA and protein ribonucleoprotein complex.
authors.affiliation: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan.
authors.forename: Daijiro
authors.initials: D
authors.lastname: Takeshita
authors.forename: Seisuke
authors.initials: S
authors.lastname: Yamashita
authors.forename: Kozo
authors.initials: K
authors.lastname: Tomita
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D017908:Allolevivirus / Q000201:enzymology*; D001483:Base Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D026723:Polyadenylation; D011485:Protein Binding; D011777:Q beta Replicase / Q000737:chemistry*; D012367:RNA, Viral / Q000737:chemistry*; D013379:Substrate Specificity; D014764:Viral Proteins / Q000737:chemistry*
chemical_list: D012367:RNA, Viral; D014764:Viral Proteins; D000255:Adenosine Triphosphate; D011777:Q beta Replicase