Coordinated function of cellular DEAD-box helicases in suppression of viral RNA recombination and maintenance of viral genome integrity.

Chingkai Chuang,Peter D Nagy,K Reddisiva Prasanth,Aiming Wang

doi:10.1371/journal.ppat.1004680

Abstract

The intricate interactions between viruses and hosts include an evolutionary arms race and adaptation that is facilitated by the ability of RNA viruses to evolve rapidly due to high frequency mutations and genetic RNA recombination. In this paper, we show evidence that the co-opted cellular DDX3-like Ded1 DEAD-box helicase suppresses tombusviral RNA recombination in yeast model host, and the orthologous RH20 helicase functions in a similar way in plants. In vitro replication and recombination assays confirm the direct role of the ATPase function of Ded1p in suppression of viral recombination. We also present data supporting a role for Ded1 in facilitating the switch from minus- to plus-strand synthesis. Interestingly, another co-opted cellular helicase, the eIF4AIII-like AtRH2, enhances TBSV recombination in the absence of Ded1/RH20, suggesting that the coordinated actions of these helicases control viral RNA recombination events. Altogether, these helicases are the first co-opted cellular factors in the viral replicase complex that directly affect viral RNA recombination. Ded1 helicase seems to be a key factor maintaining viral genome integrity by promoting the replication of viral RNAs with correct termini, but inhibiting the replication of defective RNAs lacking correct 5’ end sequences. Altogether, a co-opted cellular DEAD-box helicase facilitates the maintenance of full-length viral genome and suppresses viral recombination, thus limiting the appearance of defective viral RNAs during replication.

Highlights

RNA viruses replicate inside cells and they require many cellular factors to complete their infection cycle
Similar to viral replication that greatly depends on subverted cellular proteins, viral genetic recombination is affected by host factors based on genome-wide screens with tomato bushy stunt virus (TBSV) in yeast model host
We show evidence, in yeast, plants and in vitro, that co-opted cellular helicases by TBSV affect viral recombination through suppressing template-switching and replication

Summary

Introduction

RNA viruses replicate inside cells and they require many cellular factors to complete their infection cycle. Cellular and environmental factors affect viral RNA recombination, which is a process that joins two or more noncontiguous segments of the same RNA or two separate RNAs together [4,5]. Recombination could alter viral genomes by introducing insertions or duplications, combining new sequences, or leading to deletions or rearrangements. RNA recombination functions to repair truncated or damaged viral RNA molecules [2,5,6,7]. Viral RNA recombination can affect virus population dynamics, contribute to virus variability, as well as function in genome repair that maintains the infectivity of RNA viruses [3,4]

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Conclusion