IDENTIFICATION OF A NOVEL CA2-STIMULATED S6-KINASE IN RAT-LIVER()

Extracellular calcium addition transiently stimulated two S6 peptide k inase activities in isolated rat hepatocytes, Mono Q chromatography re vealed that the activities eluting at 0.15 M NaCl and 0.18 M NaCl were stimulated 4-fold and 2-fold, respectively, The kinase stimulated by calcium was a 40000-Mr S6 peptide kinase, as demonstrated by partial p urification from whole liver, The protein kinase did not crossreact wi th antibodies directed against the N- or C-terminal part of p70 riboso mal S6 kinase (p70(S6K)) and the C-terminal part of p90 ribosomal S6 k inase (p90(rsk)), Following digestion of 40000-Mr S6 peptide kinase wi th trypsin, six peptides were sequenced, There was no similarity with the sequences of p70(S6K) and p90(rsk), Moreover, the obtained sequenc es could not be identified in the SwissProt or EMBL-genebank databases , suggesting that 40000-Mr S6 peptide kinase probably represents a nov el protein kinase. (C) 1997 Academic Press.