THE ETHYLENE RESPONSE MEDIATOR ETR1 FROM ARABIDOPSIS FORMS A DISULFIDE-LINKED DIMER

Mutations in the ETR1 gene of the higher plant Arabidopsis confer inse nsitivity to ethylene, indicating a role for the gene product in ethyl ene signal perception and transduction. The ETR1 gene product has an a minoterminal hydrophobic domain and a carboxyl-terminal domain showing homology to the two-component signal transduction proteins of bacteri a. me report here that in both its native Arabidopsis and when transge nically expressed in yeast, the ETR1 protein is isolated from membrane s as a dimer of 147 kDa. Treatment with the reducing agent dithiothrei tol converted the dimer to a monomer of 79 kDa, indicative of a disulf ide linkage between monomers. Expression of truncated versions of ETR1 in yeast confirmed that the high molecular mass form is a homodimer a nd demonstrated that the aminoterminal region of ETR1 is necessary and sufficient for this dimerization. Site-directed mutagenesis of two cy steines near the amino terminus of ETR1 prevented formation of the cov alently linked dimer in yeast, consistent with a role in disulfide bon d formation. These data indicate that ETR1 may use a dimeric mechanism of signal transduction in a manner similar to its bacterial counterpa rts but with the additional feature of a disulfide bond between monome rs.