Tomato yellow vein streak virus (ToYVSV) is a tentative begomovirus (Family Geminiviridae) species that seriously affects tomato and potato production in Brazil. Here, we have determined the genomic and biological characteristics of a ToYVSV isolate (Ba3) from a potato plant sampled in Rio Grande do Sul State, Brazil. The DNA-A nucleotide sequence of Ba3 and another previously reported ToYVSV isolate share 89.7% sequence identity. These ToYVSV isolates should be classified as a new species in that they are most closely related to Soybean blistering mosaic virus with which they share only approximately 80% identity. Cloned constructs containing 1.5 mer copies of the ToYVSV genomic components were found, by biolistic bombardment, to be infectious in at least 11 plant species in 2 families (Solanaceae and Malvaceae). Symptoms on tomato and potato plants were identical to those originally observed on field-infected plants. ToYVSV was also sap-transmissible from Nicotiana benthamiana to N. benthamiana and tomato, but not to potato plants.