HIV-1 Proteinase as Structural Model of Intercellular Transport Proteins of Plant Viruses

Intercellular movement of viral infections of plants requires a virus-encoded protein. Alignment of amino acid sequences of central conserved regions of such proteins produced a sequence profile that resembled that of lentiviral proteinases. The known three-dimensional structure of the proteinase encoded by the human immunodeficiency virus-1 (HIV-I) may serve as a model for the three-dimensional structure of the central region of the plant viral proteins. Secondary structures predicted for the plant viral proteins from their amino acid sequences correlate well with those predicted from a proteinase model. In addition, the positions of temperature-sensitive and resistance-breaking mutations in the intercellular transport protein of tobacco mosaic virus are consistent with a structural similarity between the plant viral proteins and the lentiviral proteinases. In a suggested model, the dimeric proteinase-similar domain serves as tether for the attachment of N- and C-terminal domains. The C-terminal domain may be an RNA-binding domain. The similarity was used to assign intercellular transport function to a previously unidentified coding region of the genomes of bacilliform DNA viruses.