The product of ORF III in cauliflower mosaic virus interacts with the viral coat protein through its C-terminal proline rich domain

Using the yeast two-hybrid system, we show that the ORF III product of cauliflower mosaic virus (pIII) interacts through its C-terminus with the viral coat protein. The last five amino acids of pIII were essential for the interaction and virus infectivity. Deletion of the last three amino acids or the mutation F129A decreased the strength of the interaction by 90%. We further show that pIII is closely associated with virus particles found in the inclusion bodies of infected plants but not in viral particles released from the inclusion bodies by urea treatment.