Ethylene receptor related to bacterial two-component regulators. Acts as a redundant negative regulator of ethylene signaling. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Binds 1 copper ion per dimer. Homodimer; disulfide-linked. Heteromer with ETR1. Expressed in etiolated seedlings, leaves, stems, roots, flowers, embryos, anthers, carpels and ovules. By ethylene. Autophosphorylated on both His and Ser residues in the presence of manganese. Loss of His autophosphorylation in the presence of both manganese and magnesium. No visible phenotype in ethylene response; due to the redundancy with ETR1. Ers1 and etr1 double mutants display a constitutive ethylene-response phenotype. Belongs to the ethylene receptor family.