Inhibition of Rous sarcoma virus production by formycin

The effect of formycin, an adenosine analog, on the growth of chick embryo fibroblasts and on Rous sarcoma virus (RSV) production was studied. An adverse effect on cell proliferation was observed in the presence of 10 microM formycin. Treatment with 5 microM formycin for 24 hr reduced by a factor of about 1000 the yield of infections progeny whereas the cell growth remained unaltered. Moreover the few particles released in the presence of formycin showed a markedly decreased ability to synthesize viral cDNA. This impairment was shown to be related to a nonfunctional primer tRNA.     

The nucleotide sequence of <Emphasis Type="Italic">Watermelon mosaic virus</Emphasis> (WMV, <Emphasis Type="Italic">Potyvirus</Emphasis>) reveals interspecific recombination between two related potyviruses in the 5′ part of the genome

Summary. Watermelon mosaic virus (WMV, Potyvirus) is a potyvirus with a worldwide distribution, mostly in temperate and mediterranean regions. According to the partial sequences that were available, WMV appeared to share high sequence similarity with Soybean mosaic virus (SMV), and it was almost considered as a strain of SMV in spite of its different and much broader host range. Like SMV, it was also related to legume-infecting potyviruses belonging to the Bean common mosaic virus (BCMV) subgroup. In this paper we obtained the full-length sequence of WMV, and we confirmed that this virus is very closely related to SMV in most of its genome; however, there is evidence for an interspecific recombination in the P1 protein, as the P1 of WMV was 135 amino-acids longer than that of SMV, and the N-terminal half of the P1 showed no relation to SMV but was 85% identical to BCMV. This suggests that WMV has emerged through an ancestral recombination event, and supports the distinction of WMV and SMV as separate taxonomic units.     

Durable virus resistance in plants through conventional approaches: a challenge

Breeding for virus resistance is often considered the most efficient and simplest way to avoid the losses due to plant virus diseases. Resistance mechanisms are very diverse and interact with various stages of the virus cycle in the host plant. Resistances may also differ in their specificity, stability and durability. Breeding for resistance is a long and costly process, therefore to be cost effective it should provide durable protection. Three pathosystems are discussed to illustrate some of the field and laboratory approaches that can be used to assess resistance durability: Cucumber mosaic virus-specific resistance in melon, Zucchini yellow mosaic virus tolerance in zucchini squash, and extreme resistance to Potato virus X in potato. The possibility of predicting resistance durability is discussed in relation to the nature of the resistance, the genetic changes required for a virus to overcome the resistance and the effects of such changes on virus fitness.