THE PROTEINS AND FUNCTIONS OF PLANT PARARETROVIRUSES - KNOWNS AND UNKNOWNS

Two main classes of plant pararetroviruses exist: the icosahedral caul imoviruses and the bacilliform badnaviruses. In addition, the icosahed ral cassava vein mosaic virus might constitute a separate group, becau se it differs from the other caulimoviruses in several aspects. Both g roups of viruses contain genes homologous to the gag and pol genes of animal retroviruses. The genes for insect transmission and movement, o n the other hand, have no counterparts in retroviruses but are related to the corresponding genes of plant RNA viruses. In addition, caulimo viruses, and probably the rice tungro badnavirus, have regulatory gene s. The architecture and functions of the plant pararetrovirus gene pro ducts are compared and discussed.