Efficient cloning of cDNA from grapevine leafroll-associated virus 4 and demonstration of probe specificity by the viral antibody

Using a random-PCR method, a cDNA clone (LR4) was constructed from the replicative form dsRNA of grapevine leafroll-associated virus 4 (GLRaV-4). Northern blot analysis showed hybridization of LR4 to dsRNA in an extract of a Thompson Seedless grapevine clone from which GLRaV-4 was isolated originally by Hu et al. (1990). The cDNA clone was sequenced and shown to be specific to GLRaV-4 by reverse-transcription-PCR using GLRaV-4 particles enriched by the virus antibody coupled to magnetic beads. Reverse-transcription-PCR was used successfully to screen different varieties of grapevines for the virus. Western blot analysis of GLRaV-4 extracts from different varieties of infected grapevines revealed two distinct species of capsid protein with estimated Mr of either 35 500 or 38 000 depending on the variety used. Both proteins reacted with polyclonal as well as monoclonal antibodies.