| dc.description.abstract | Potyviruses belong to the picornavirus-like supergroup of positive-strand RNA viruses 6. Potyviruses form the largest and most economically important group of plant viruses 7. This group includes such viruses as potato Y virus, tobacco vein mottling virus, plum pox virus, and tobacco etch virus (TEV), which is the model system used for this research. Potyviruses have a filamentous structure consisting of numerous capsid proteins surrounding a single molcule of RNA with a virus encoded protein attached to 5’ end. The single-stranded RNA of 10,000 nucleotides encodes a single polyprotein which autocatalytically cleaves itself into nine proteins. These nine proteins provide the means by which the virus replicates in infected cells, moves to neighboring cells, and moves to other parts of the plant through the vascular tissue of the plant. Among the viral proteins are three proteases PI, HC-Pro, and NIa. One of these, HC-Pro, is the focus of this study.
HC-Pro (Helper component-protease) protein, which aggregates as amorphous inclusion bodies within the cytoplasm of infected plant cells 4, has at least two functional domains and possibly a third. The carboxy terminal end of the protein contains the protease domain. This protease function cleaves the carboxy terminus of HC-Pro from the neighboring P3 protein which has not yet been assigned a function. The amino terminal helper component domain, in particular lysine 54, allows the virus to be transmitted from plant to plant via aphids 11. This domain is not needed for viral replication or movement between plant cells, although deletions of this domain greatly decrease the efficiency of viral replication 7. This decrease in replication efficiency suggests that HC-Pro may function as an accessory factor in replication. The presence of a group of conserved cysteine residues suggests the possibility of a metal binding motif analogous to the zinc finger motif of several eukaryotic transcription factors 12, '>. In addition to the two terminal domains, the central part of the protein may constitute a third functional domain. This region, although well conserved in potyviruses, is absent in related viruses such as barley yellow mosaic virus (BaYMV) and the chestnut blight hypovirulence-associated double stranded RNA (HAV) 8. In conjunction with the N-terminal domain of HC-Pro, this central region may function as an accessory factor to the viral replication complex.
To investigate this possibility, five highly conserved sites were identified within the area by comparison to the amino acid sequences of related potyviruses. Two of these sites (coding for three amino acids each) were selected for mutagenesis. Here the preliminary characterization of the replication and movement characteristics of these mutants are reported. | en |
