STRUCTURE-FUNCTION RELATIONSHIP BETWEEN TOBACCO MOSAIC-VIRUS COAT PROTEIN AND HYPERSENSITIVITY IN NICOTIANA-SYLVESTRIS

Alterations in the structure of the tobacco mosaic virus (TMV) coat pr otein affect the elicitation of the N' gene hypersensitive response (H R) in Nicotiana sylvestris. To investigate this structure-function rel ationship, amino acid substitutions with predicted structural effects were created throughout the known structure of the TMV coat protein. S ubstitutions that resulted in the elicitation of the HR resided within and would predictably interfere with interface regions located betwee n adjacent subunits in ordered aggregates of coat protein. Substitutio ns that did not result in the elicitation of the HR were either conser vative or located outside these interface regions. In vitro analysis o f coat protein aggregates demonstrated HR-eliciting coat proteins to h ave reduced aggregate stability in comparison with non-HR-eliciting co at proteins and a correlation existed between the strength of the elic ited HR and the ability of a substitution to interfere with ordered ag gregate formation. This finding corresponded with the predicted struct ural effects of HR-eliciting substitutions. Radical substitutions that predictably disrupted coat protein tertiary structure were found to p revent HR elicitation. These findings demonstrate that structural alte rations that affect the stability of coat protein quaternary structure but not tertiary structure lead to host cell recognition and HR elici tation. A model for HR elicitation is proposed, in which disassembly o f coat protein aggregates exposes a host ''receptor'' binding site.