| Here we showed a novel interaction between PKR and apoptosis signal regulating kinase 1 ( ASK 1 ) , one of the members of the mitogen activated protein kinase kinase kinase family , which is activated in response to a variety of apoptosis inducing stimuli . ^^^ PKR and ASK 1 showed predominant cytoplasmic localization in COS 1 cells transfected with both cDNAs , and coimmunoprecipitated from the cell extracts . ^^^ A dominant negative mutant of PKR ( PKR KR ) inhibited both the apoptosis and p 38 activation induced by ASK 1 in vivo . ^^^ Consistently , PKR KR inhibited the autophosphorylation of ASK 1 in vitro , and exposure to poly ( 1 ) poly ( C ) increased the phosphorylation of ASK 1 in vivo . ^^^ These results indicate the existence of a link between PKR and ASK 1 , which modifies downstream MAPK . . ^^^ |