STRUCTURAL AND FUNCTIONAL CONSERVATION OF THE TOBAMOVIRUS COAT PROTEIN ELICITOR-ACTIVE SITE

Elicitation of the N' gene hypersensitive response (HR) in Nicotiana s ylvestris is dependent upon specific structural elements of an elicito r active site located along the right face of the tobacco mosaic tobam ovirus (TMV) coat protein (CP) (Z. Taraporewala and J. N. Culver, Plan t Cell 8:169-178, 1996), In this study, the functional and structural conservation of this site was examined in three different tobamovirus CPs that vary widely in sequence homology but share a common three-dim ensional fold, Results demonstrate that the CPs of TMV-U2, Odontogloss um ringspot, and cucumber green mottle mosaic tobamoviruses elicit the N' gene HR with strength and temperature stability comparable to the TMV elicitor CP P20L. Within each CP amino acid substitutions designed to disrupt tertiary structure interfered with N' gene elicitation, Su bstitutions of selected surface residues within the previously identif ied elicitor active site of each CP inhibited HR elicitation, while su bstitutions outside of this region did not alter elicitor activity, Co mparisons of surface characteristics within the elicitor active sites of the different CPs revealed the presence of a conserved central hydr ophobic cavity, Surface features at the periphery of this cavity showe d less conservation, which may explain the unequal ability of some sub stitutions in this region to alter the elicitor activity of the differ ent CPs, These findings suggest N' gene specificity is dependent upon the three-dimensional fold of CP as well as upon specific surface feat ures within the elicitor active site.