A novel protein kinase, designated PKN, was identified by molecular cloning from a human hippocampus cDNA library. PKN consists of 942 amino acids with a calculated molecular mass of 103,925 daltons. PKN has leucine zipper-like sequences in its amino terminal region and contains a catalytic domain that shows strong similarity to that of protein kinase C family. Northern blot analysis indicates PKN is expressed ubiquitously in human tissues. Antisera against PKN identified a 120K dalton protein on SDS polyacrylamide gel electrophoresis when PKN was expressed in the insect cells or COS7 cells. Recombinant PKN revealed an intrinsic protein kinase activity associated with a 120K protein. This activity was abolished by mutation of the lysine residue in the potential ATP binding site.