Precursor of cdk5 activator, the 23 kDa subunit of tau protein kinase II: Its sequence and developmental change in brain

Abstract
Tau protein kinase II (TPKII) is shown by immunoprecipitation to be a complex composed of two subunits, a catalytic subunit, cdk5, and regulatory subunit, p23. By sequence analysis of p23 CDNA, p23 was found to occupy a region from the 99th amino acid residue to the C‐terminus of a novel protein with a molecular weight of 34,000 Da, suggesting that this 34 kDa protein is a precursor of p23 (pre‐p23). These findings suggest that p23 results from the processing of the precursor protein, pre‐p23. The precursor mRNA was expressed most abundantly in rat brain just before and after birth. Expression of pre‐p23, but not of cdk5, mRNA changed, coinciding with the developmental change of TPKII activity, suggesting that its expression controls the phosphorylation of tau by the TPKII/TPKI system in the neonatal brain. p23 appears to be a cdk5 activator in neuronal cells.