codon. The third segment, RNA-TGB encodes triple gene block of movement proteins, TGB1, TGB2, TGB3, and 8K protein which is a viral suppressor of RNA silencing. Pathogenesis The vector for PMTV is a protist, S. subterranea. As S. subterranea infects the roots of potatoes, the virus is given access to the root cells and starts its habitation of the plant. By taking control of the cell's cellular machinery, the virus can replicate. The virus then moves onto more potato cells and spreads systemically through the plant. The systemic movement of PMTV is facilitated in large by a protein named TRIPLE GENE BLOCK1 (TGB1) which has an internal domain spurring transportation of the virus to neighboring cells, and an N-terminal domain used for long-distance (systemic) travel. This N-terminal domain of TGB1 has shown some promise as a target to limit systemic infection of the pathogen in N. benthamiana, since systemic infection requires an interaction between a molecule called importin-a within the host plant and the N-terminal domain. Of the three positive-sense RNA molecules used by PMTV, there is one thought to code for a virulence factor protein. The other two molecules code for a polymerase and a coat protein both of which are necessary for the survival of the virus. RNA-TGB is a gene with 4 open reading frames (ORFs); the first three overlapping ORFs form an area called the triple gene block. This 3 frame block codes for essential movement factor proteins that facilitate cell-to-cell movement. The fourth ORF codes for another cysteine-rich protein that increases virulence and has some RNA silencing suppressive activity. See also Viral diseases of potato References External links ICTVdB - The Universal Virus Database: Potato mop-top virus Family Groups - The Baltimore Method Virgaviridae Viral plant pathogens and diseases Potato diseases