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Recent studies suggest that CaM kinase II is involved in light-induced phase delays and induction of Per1 and Per2 genes in the hamster suprachiasmatic nucleus (SCN) (Yokota et al.,2001). We focused on intracellular mechanisms of the CaM kinase II-induced mPer1 gene expression. Immunoblotting and immunohistochemical analyses with isoform-specific antibodies against different isoforms of CaM kinase II and CaM kinase IV showed abundant expression of the delta isoform of CaM kinase II without significant expression of CaM kinase IV in the lateral ventral region of the rat SCN. We next defined the CaM kinase II-responsive region on the mPer1 promoter using a luciferase reporter gene assay. Transfection of the constitutively-active CaM kinase IIdelta greatly increased mPer1 promoter activity in NG108-15 cells and increased activity slightly but significantly in NB2A and C6 glioma cells. Similarly, transfection of a constitutively-active MEKK, an upstream kinase of mitogen-activated protein kinase (MAPK), greatly increased promoter activity in NB2A cells. Deletion and mutation analyses of the mPer1 promoter revealed that a 5'-GAGGGG-3' sequence motif near exon 1B, in which several zinc finger proteins seem to bind, was essential for the CaM kinase II-induced activation of the mPer1 promoter. These results suggest that CaM kinase IIdelta but not CaM kinase IV plays an essential role for mPer1 expression through the 5'-GAGGGG-3' motif on the mPer1 promoter., (Copyright 2003 Wiley-Liss, Inc.)