TI - PHAS-I as a link between mitogen -activated protein kinase and translation initiation . AB - PHAS-I is a heat-stable protein ( relative molecular mass approximately 12,400 ) found in many tissues . It is rapidly phosphorylated in rat adipocytes incubated with insulin or growth factors . Nonphosphorylated PHAS-I bound to initiation factor 4E (eIF-4E) and inhibited protein synthesis . Serine-64 in PHAS-I was rapidly phosphorylated by mitogen-activated ( MAP ) kinase , the major insulin-stimulated PHAS-I kinase in adipocyte extracts . Results obtained with antibodies , immobilized PHAS-I , and a messenger RNA cap affinity resin indicated that PHAS-I did not bind eIF-4E when serine-64 was phosphorylated . Thus , PHAS-I may be a key mediator of the stimulation of protein synthesis by the diverse group of agents and stimuli that activate MAP kinase .