The casein kinase I (CKI) family consists of widely distributed monomeric Ser/Thr protein kinases that have a preference for acidic substrates. Four mammalian isoforms are known. A full length cDNA encoding the CKIα isoform was cloned from a rabbit skeletal muscle cDNA library and was utilized to construct a bacterial expression vector. Active CKIα was expressed in Escherichia coli as a polypeptide of Mr 36,000. The protein kinase phosphorylated casein, phosvitin and a specific peptide substrate (D4). The enzyme was inhibited by the isoquinolinesulfonamide CKI-7, half-maximally at 70 μM. Heparin inhibited phosphorylation of the D4 peptide or phosvitin by CKIα. Polylysine activated when the D4 peptide was the substrate but had no effect on phosvitin phosphorylation. It is becoming clear that the individual CKI isoforms have different kinetic properties and hence could have quite distinct cellular functions.
|Original language||English (US)|
|Number of pages||6|
|Journal||Biochemical and Biophysical Research Communications|
|State||Published - Dec 15 1992|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology