A class of protein kinases in the plant Arabidopsis thaliana has been identified which has biochemical characteristics similar to those of the animal receptor protein kinases. These plant protein kinases are membrane-associated, glycosylated, exhibit a preference for Mn2+ relative to Mg2+, and range from 115 to 135 kDa when identified by renaturation after protein blotting. Evidence is presented that the TMK1 protein, a receptor-like protein kinase identified in Arabidopsis from its cloned gene, is also glycosylated in its native form, and shows a preference for Mn2+ over Mg2+ when assayed for kinase activity. All of the plant receptor-like protein kinases identified phosphorylate only serine and threonine residues.
