A HEAT-STRESS PULSE INACTIVATES A 50 KDA MYELIN BASIC-PROTEIN KINASE IN TOMATO

The involvement of kinases in heat stress signaling in tomato cells wa s studied by in gel kinase assays using myelin basic protein as substr ate, and by in vitro phosphorylation assays in Mono Q fractions of tom ato cell lysates. A kinase with an apparent molecular mass of approxim ately 50 kDa is rapidly deactivated upon heat stress as judged from in gel kinase assays. Cycloheximide treatment increases kinase activity, but concomitant heat treatment abolishes cycloheximide-induced activa tion. Kinase activity from untreated cells was recovered at about 130 and 250 mM NaCl from Mono Q columns.