PHOSPHORYLATION OF CREB BY CAM-KINASE-IV ACTIVATED BY CAM-KINASE-IV KINASE

Previous reports have shown that CaM-kinase IV can phosphorylate the t ranscription factor CREB in vitro on Ser133. Furthermore, transfected CaM-kinase IV can activate CREB-dependent transcription, but at a lowe r efficiency than the cAMP-kinase. In this paper we examine the kineti cs and site-specificity of CREB phosphorylation in vitro by CaM-kinase IV after its phosphorylation and activation by a newly discovered bra in CaM-kinase IV kinase. Our results show that activated CaM-kinase IV has the same Km (1-5 mu M) for CREB phosphorylation, but the Vmax is about 30-fold higher than with non-activated CaM-kinase IV. Activated CaM-kinase IV still shows specificity for phosphorylation of Ser133, t he site necessary for transactivation by CREB. It is likely that the l ower efficiency of transcriptional activation by transfected CaM-kinas e IV in previous studies was due to the fact that the CaM-kinase IV wa s not activated by CaM-kinase IV kinase. (C) 1995 Academic Press, Inc.