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 caul iflower mosaic virus (pIII) interacts through its C-terminus with the viral coat protein. The last five amino acids of pIII were essential for the int eraction and virus infectivity. Deletion of the last three amino acids or t he mutation F129A decreased the strength of the interaction by 90%. We furt her show that pIII is closely associated with virus particles found in the inclusion bodies of infected plants but not in viral particles released fro m the inclusion bodies by urea treatment.