An active replication complex of citrus exocortis viroid (CEV) was isolated as a 
chromatin-enriched fraction of infected tomato leaf with CEV RNA synthesis 
activity. This activity was solubilised from the chromatin with ammonium 
sulphate, but not with sarkosyl. Nucleoprotein complexes in the soluble fraction 
which bound to a monoclonal antibody to the carboxy terminal domain of the 
largest subunit of RNA polymerase II (8WG16) were affinity purified 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 evidence of an 
association in vivo between host RNA polymerase II and CEV.