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

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.