Citrus exocortis viroid RNA is associated with the largest subunit of RNA polymerase II in tomato in vivo

An active replication complex of citrus exocortis viroid (CEV) was isolated as a chromatin-enriched fraction of infected tomato leaf with CEV RNA synt hesis activity. This activity was solubilised from the chromatin with ammon ium sulphate, but not with sarkosyl. Nucleoprotein complexes in the soluble fraction which bound to a monoclonal antibody to the carboxy terminal doma in of the largest subunit of RNA polymerase II (8WG16) were affinity purifi ed and contained plus- and minus-sense CEV RNA. The results support a role for RNA polymerase II in viroid replication and provide the first direct ev idence of an association in vivo between host RNA polymerase II and CEV.