RNA-dependent RNA polymerase

About: RNA-dependent RNA polymerase is a research topic. Over the lifetime, 13904 publications have been published within this topic receiving 767954 citations. The topic is also known as: RdRp & RNA replicase.

The eightfold path to non-enzymatic RNA replication

Abstract: The first RNA World models were based on the concept of an RNA replicase - a ribozyme that was a good enough RNA polymerase that it could catalyze its own replication. Although several RNA polymerase ribozymes have been evolved in vitro, the creation of a true replicase remains a great experimental challenge. At first glance the alternative, in which RNA replication is driven purely by chemical and physical processes, seems even more challenging, given that so many unsolved problems appear to stand in the way of repeated cycles of non-enzymatic RNA replication. Nevertheless the idea of non-enzymatic RNA replication is attractive, because it implies that the first heritable functional RNA need not have improved replication, but could have been a metabolic ribozyme or structural RNA that conferred any function that enhanced protocell reproduction or survival. In this review, I discuss recent findings that suggest that chemically driven RNA replication may not be completely impossible.

Dbp5p, a cytosolic RNA helicase, is required for poly(A) + RNA export

Abstract: The DBP5 gene encodes a putative RNA helicase of unknown function in the yeast Saccharomyces cerevisiae. It is shown here that Dbp5p is an ATP-dependent RNA helicase required for polyadenylated [poly(A)+] RNA export. Surprisingly, Dbp5p is present predominantly, if not exclusively, in the cytoplasm, and is highly enriched around the nuclear envelope. This observation raises the possibility that Dbp5p may play a role in unloading or remodeling messenger RNA particles (mRNPs) upon arrival in the cytoplasm and in coupling mRNP export and translation. The functions of Dbp5p are likely to be conserved, since its potential homologues can be found in a variety of eukaryotic cells.

Globin mRNAs are primers for the transcription of influenza viral RNA in vitro

Abstract: Because influenza viral RNA transcription in vitro is greatly enhanced by the addition of a primer dinucleotide, ApG or GpG, we have proposed that viral RNA transcription in vivo requires initiation by primer RNAs synthesized by the host cell, specifically by RNA polymerase II, thereby explaining the α-amanitin sensitivity of viral RNA transcription in vivo. Here, we identify such primer RNAs, initially in reticulocyte extracts, where they are shown to be globin mRNAs. Purified globin mRNAs very effectively stimulated viral RNA transcription in vitro, and the resulting transcripts directed the synthesis of all the nonglycosylated virus-specific proteins in micrococcal nuclease-treated L cell extracts. The viral RNA transcripts synthesized in vitro primed by ApG also directed the synthesis of the nonglycosylated virus-specific proteins, but the globin mRNA-primed transcripts were translated about 3 times more efficiently. The translation of the globin mRNA-primed, but not the ApG-primed, viral RNA transcripts was inhibited by 7-methylguanosine 5′-phosphate in the presence of S-adenosylhomocysteine, suggesting that the globin mRNA-primed transcripts contained a 5′-terminal methylated cap structure. We propose that this cap was transferred from the globin mRNA primer to the newly synthesized viral RNA transcripts, because no detectable de novo synthesis of a methylated cap occurred during globin mRNA-primed viral RNA transcription. Preliminary experiments indicate that other purified eukaryotic mRNAs also stimulate influenza viral RNA transcription in vitro.

Mutational Analysis of Hepatitis C Virus Nonstructural Protein 5A: Potential Role of Differential Phosphorylation in RNA Replication and Identification of a Genetically Flexible Domain

Abstract: Nonstructural protein 5A of the hepatitis C virus (HCV) is a highly phosphorylated molecule implicated in multiple interactions with the host cell and most likely involved in RNA replication. Two phosphorylated variants of NS5A have been described, designated according to their apparent molecular masses (in kilodaltons) as p56 and p58, which correspond to the basal and hyperphosphorylated forms, respectively. With the aim of identifying a possible role of NS5A phosphorylation for RNA replication, we performed an extensive mutation analysis of three serine clusters that are involved in phosphorylation and hyperphosphorylation of NS5A. In most cases, alanine substitutions for serine residues in the central cluster 1 that enhanced RNA replication to the highest levels led to a reduction of NS5A hyperphosphorylation. Likewise, several highly adaptive mutations in NS4B, which is also part of the replication complex, resulted in a reduction of NS5A hyperphosphorylation too, arguing that alterations of the NS5A phosphorylation pattern play an important role for RNA replication. On the other hand, a deletion encompassing all highly conserved serine residues in the C-terminal region of NS5A that are involved in basal phosphorylation did not significantly affect RNA replication but reduced formation of p56. This region was found to tolerate even large insertions with only a moderate effect on replication. Based on these results, we propose a model of the role of NS5A phosphorylation in the viral life cycle.