cloning expression and localization of 230kda phosphatidylinositol 4kinase a phosphatidylinositol pi 4kinase cdna was cloned from a rat brain cdna library this cdna encoded a protein of 2041 amino acids with a calculated molecular weight of 231317 the deduced amino acid sequence shared the identity of 523 and 344 in the presumed catalytic domain with two yeast pi 4kinases stt4 and pik1 respectively and showed 317 identity to p110alpha subunit of rat pi 3kinase in the same domain in addition a 3 half coding region of the present cdna was 896 identical to and its deduced amino acid sequence was 982 identical to the sequence for p14kalpha a recently reported human pi 4kinase of type ii suggesting that p14kalpha is an alternative form of the present pi 4kinase molecule the present cdna contained sequences encoding the ankyrin repeat domain lipid kinase unique domain pleckstrin homology domain presumed lipid kinaseprotein kinase homology domain prolinerich region and sh3 domain by examining pi kinase activity in transfected cos7 cells using the epitope tag immunoprecipitation as well as the conventional way the product phosphatidylinositol phosphate was identified as phosphatidylinositol 4phosphate but not phosphatidylinositol 3phosphate this pi 4kinase activity was markedly enhanced in the presence of triton x100 but relatively insensitive to inhibition by adenosine by epitope tag immunohistochemistry the immunoreactivity for this pi 4kinase molecule was largely localized in close association with the membranes of the golgi vesicles and vacuoles by in situ hybridization analysis the expression of mrna for this pi 4kinase was evident throughout the gray matter of entire brain with higher expression intensity in fetal brain these data imply that this novel pi 4kinase is involved in some processes essential to neuronal differentiation and maturation including the synaptogenesis and synaptic plasticity