PARALLEL SIGNAL-PROCESSING AMONG MAMMALIAN MAPKS

The intracellular signalling field is dominated by the mitogen-activat ed protein kinase (MAPK) cascade and its control, which involves the s mall GTPase Ras and sequential kinase activation. Until recently, ERK1 and ERK2 were the only cloned and well-characterized mammalian MAPKs; diverse ligand-stimulated, proline-directed protein phosphorylation e vents were attributed to these kinases, The recent discovery of two ot her MAPK subtypes, the JNK/SAPK subfamily and p38/RK (mammalian equiva lents of HOG1 in yeast), reveals extreme complexity within the family and, most intriguingly, the existence in mammalian cells of parallel M APK cascades that can be activated simultaneously.