Potyvirus Isolation and RNA Extraction

The Potyviridae are the largest single group of plant viruses, and as such are the most important from an economic standpoint. There are nearly 200 distinct recognized species or other viruses that are possible or probable members of the group. Two recent books provide an excellent and in depth review of the Potyviridae (1 ,2 ). Generally, they are filamentous particles of ca. 11–12 � 680–900 nm. The single-stranded, message sense RNA molecule of the virus genome is encapsidated by single species of CP of ca. 30–36 kDa. This RNA (ca. 8500–9800 nucleotides) is polyadenylated and also contains a VPg covalently bound to the 5′ end. Coat protein amino acid sequences show significant homology, particularly within the core region. Virions are approx 5% RNA and 95% protein by weight. The virus RNA is translated initially as a large polyprotein that is autoproteolytically cleaved to provide the mature viral proteins (Fig. 1 ).