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The structure of EBOV L-VP35-RNA complexThe structure of EBOV L-VP35-RNA complex
Structural highlights
FunctionA0A1C4HDB0_9MONO RNA-directed RNA polymerase that catalyzes the replication of viral genomic RNA. The template is composed of the viral RNA tightly encapsidated by the nucleoprotein (N). The replicase mode is dependent on intracellular N protein concentration. In this mode, the polymerase replicates the whole viral genome without recognizing transcriptional signals, and the replicated genome is not caped or polyadenylated.[ARBA:ARBA00003132][PIRNR:PIRNR037548] RNA-directed RNA polymerase that catalyzes the transcription of viral mRNAs, their capping and polyadenylation. The template is composed of the viral RNA tightly encapsidated by the nucleoprotein (N). The viral polymerase binds to the genomic RNA at the 3' leader promoter, and transcribes subsequently all viral mRNAs with a decreasing efficiency. The first gene is the most transcribed, and the last the least transcribed. The viral phosphoprotein acts as a processivity factor. Capping is concommitant with initiation of mRNA transcription. Indeed, a GDP polyribonucleotidyl transferase (PRNTase) adds the cap structure when the nascent RNA chain length has reached few nucleotides. Ribose 2'-O methylation of viral mRNA cap precedes and facilitates subsequent guanine-N-7 methylation, both activities being carried by the viral polymerase. Polyadenylation of mRNAs occur by a stuttering mechanism at a slipery stop site present at the end viral genes. After finishing transcription of a mRNA, the polymerase can resume transcription of the downstream gene.[PIRNR:PIRNR037548] Publication Abstract from PubMedNon-segmented negative-strand RNA viruses (nsNSVs) including Ebola virus (EBOV), rabies virus, human respiratory syncytial virus and pneumoviruses can cause respiratory infections, hemorrhagic fever and encephalitis in the humans and animals, and are considered as substantial health and economic burden worldwide(1). Replication and transcription of the viral genome are executed by the large L polymerase that is a promising target for the development of antiviral drugs. Here, using EBOV L polymerase as a representative, we showed that de novo replication of L polymerase is controlled by the specific 3' leader sequence of EBOV genome in an enzymatic assay, and formation of at least three base pairs can effectively drive the elongation process of RNA synthesis independent of the specific RNA sequence. We then determined the high-resolution structures of EBOV L-VP35-RNA complex and found that the 3' leader RNA binds in the template entry channel with a distinctive stable bend conformation. Further mutagenesis work confirmed that the bend conformation of RNA is required for the de novo replication activity and revealed the key residues of L protein that stabilize the RNA conformation. These findings have provided a new mechanistic understanding of RNA synthesis for nsNSV polymerases, and revealed important targets for the development of antiviral drugs. Molecular mechanism of de novo replication by the Ebola virus polymerase.,Peng Q, Yuan B, Cheng J, Wang M, Gao S, Bai S, Zhao X, Qi J, Gao GF, Shi Y Nature. 2023 Sep 12. doi: 10.1038/s41586-023-06608-1. PMID:37699521[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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