Ca2+/calmodulin-dependent protein kinase I (CaM kinase I) was original
ly identified in rat brain based on its ability to phosphorylate site
1 of synapsin I. Recently a cDNA for the rat brain enzyme has been clo
ned and the primary structure elucidated [Picciotto et al. (1993), J.
Biol. Chem., 268:26512-26521]. The rat cDNA encoded a protein of 374 a
mino acids with a calculated M(r) of 41,636. Antibodies have now been
raised against the recombinant kinase expressed in E. coli as a glutat
hione-S-transferase fusion protein. Immunoblot analysis of rat cortex
lysates revealed two major immunoreactive bands of similar to M(r) 38,
000 and 42,000. Minor immunoreactive species of slightly lower M(r) we
re also detected. Two distinct CaM kinase I activities were partially
purified from rat brain and shown to correspond to the two major immun
oreactive species. A variety of immunoreactive species of M(r) 35-43,0
00 were detected in ''brain'' tissue from cow, zebra finch, goldfish,
Xenopus, lamprey, and Drosophila. In rat brain, immunocytochemistry re
vealed strong staining in cortex, hippocampus, amygdala, hypothalamus,
brain stem, and choroid plexus. The labelling was mainly observed in
neuropil but clusters of intensely labelled neuronal cell bodies were
also detected all along the neuraxis. Neuronal nuclei and glial cells
did not appear to be stained. Subcellular fractionation studies confir
med the cytosolic localization of the kinase in the brain. In various
rat non-neuronal tissues and in a number of cell lines, immunoreactive
species of similar to M(r) 38,000 and similar to 42,000 were detected
at lower levels than that detected in brain. The M(r) 38,000 and 42,0
00 species were also found in different ratios and at different levels
in the non-neuronal tissues. These results support a role for CaM kin
ase I in the regulation of multiple neuronal processes. Furthermore, t
he widespread cell and tissue distribution suggests that CaM kinase I
may function as a ubiquitous multi-functional protein kinase. Finally,
the multiple immunoreactive species may represent isoforms of CaM kin
ase I. (C) 1995 Wiley-Liss, Inc.