Potexvirus Isolation and RNA Extraction

The potexvirus family has at least 30 definitive and possible members, of which potato virus X (PVX) is the type member (1 –4 ). All potexviruses are morphologically similar, with flexuous, filamentous virions that range from 470 to 580 nm in length. Each virus particle contains a single-stranded, positive-sense RNA molecule, 5845–7015 nucleotides in length, which is encapsidated by 1000–1500 molecules of a single species of capsid protein (CP), with a mol wt ranging from 21 to 27 kDa (5 ). The particle has a helical structure, with 8.75 protein subunits per turn for papaya mosaic potexvirus (PMV) (6 ). The genomic RNA (gRNA) contains a cap structure at the 5′ terminus and is polyadenylated at the 3′ terminus. The N- and C-terminal regions of the capsid proteins of potexviruses are quite variable (7 ). The variability of amino acids at the N-terminus of potexvirus CP results in the low serological crossreactivity seen in potexviruses (8 ). Individual potexviruses have mol wt in the order of 35 � 10⁶ and sedimentation coefficients ranging from 100 to 130 S.