Structure Function Analysis of the helicase domain of the TMV replicase proteins

(Les Erickson, University of California, Berkeley)
Biochemical analyses in vitro analysis of recombinant p50 protein shows it can hydrolyze ATP, as predicted by the presence of ATPase/helicase motifs located in this portion of the replicase proteins. A point mutation in one of these motifs (the P-loop) abolishes ATPase activity, but does not alter cell death-inducing activity, indicating enzymatic activity is not required for elicitation. Taken together, these observations suggest that structural features of the helicase domain of the TMV replicase proteins are recognized during viral infection by N-containing plants, and this recognition elicits the defense responses.

The N gene is similar in nucleotide sequence to other gene-for-gene type of resistance genes (R genes) that confer resistance to a diverse group of pathogens including bacteria, fungi, viruses, insects and nematodes. Because of their specific role in pathogen defense and their predicted protein structures, R genes have been hypothesized to encode receptors that directly or indirectly recognize pathogen elicitor molecules and signal for defense responses. Work is ongoing using N and p50 to test these ideas.