Tombusviruses are small, plus-sense, single-stranded RNA viruses of plants. RNA-dependent RNA polymerases (RdRp) of two tombusviruses, Tomato bushy stunt virus (TBSV) and Cucumber necrosis virus (CNV), have been partially purified from infected Nicotiana benthamiana plants. The obtained RdRp complexes are capable of de novo initiation of complementary RNA synthesis using either plus- or minus-s...

Tomato bushy stunt virus (TBSV) and other tombusviruses encode a p19 protein (P19), which is a suppressor of RNAi. Wild-type TBSV or p19-defective mutants initially show a similar infection course in Nicotiana benthamiana, but the absence of an active P19 results in viral RNA degradation followed by recovery from infection. P19 homodimers sequester 21-nt virus-derived duplex siRNAs, and it is t...

Rapid evolution of RNA viruses with mRNA-sense genomes is a major concern to health and economic welfare because of the devastating diseases these viruses inflict on humans, animals, and plants. To test whether host genes can affect the evolution of RNA viruses, we used a Saccharomyces cerevisiae single-gene deletion library, which includes approximately 80% of yeast genes, in RNA recombination...

Viruses are masters of evolution due to high frequency mutations and genetic recombination. In spite of the significance of viral RNA recombination that promotes the emergence of drug-resistant virus strains, the role of host and environmental factors in RNA recombination is poorly understood. Here we report that the host Met22p/Hal2p bisphosphate-3'-nucleotidase regulates the frequency of vira...

Positive-strand RNA viruses genome replication invariably is associated with vesicles or other rearranged cellular membranes. Brome mosaic virus (BMV) RNA replication occurs on perinuclear endoplasmic reticulum (ER) membranes in ~70 nm vesicular invaginations (spherules). BMV RNA replication vesicles show multiple parallels with membrane-enveloped, budding retrovirus virions, whose envelopment ...

Avirulent genes either directly or indirectly produce elicitors that are recognized by specific receptors of plant resistance genes, leading to the induction of host defense responses such as hypersensitive reaction (HR). HR is characterized by the development of a necrotic lesion at the site of infection which results in confinement of the invader to this area. Artificial chimeras and mutants ...

Defective interfering (DI) RNAs are subviral RNAs produced during multiplication of RNA viruses by the error-prone viral replicase. DI-RNAs are parasitic RNAs that are derived from and associated with the parent virus, taking advantage of viral-coded protein factors for their multiplication. Recent advances in the field of DI RNA biology has led to a greater understanding about generation and e...

Methods are described for determining the relative mass of particles in electron microscope specimens through the measurement of photographic densities in recorded images. These methods were applied to a quantitative study of the amounts of electron stains that could be associated with the particles of tomato bushy stunt virus (BSV) and tobacco mosaic virus (TMV). In the pH range above 2 where ...

The replication of plus-strand RNA viruses depends on subcellular membranes. Recent genome-wide screens have revealed that the sterol biosynthesis genes ERG25 and ERG4 affected the replication of Tomato bushy stunt virus (TBSV) in a yeast model host. To further our understanding of the role of sterols in TBSV replication, we demonstrate that the downregulation of ERG25 or the inhibition of the ...