Preferential phosphorylation of high mobility group protein 17 in vitro by a nuclear protein kinase.

The ability of the high group proteins (HMG-1, 2, 14 and 17) to serve as substrate for protein kinases was investigated by incubating them with a cytoplasmic and nuclear kinase. In both cases phosphate was incorporated into all four HMG proteins. The amount of phosphate incorporated and the specificity for the four proteins was quite different for the two kinases. Whereas the cytoplasmic kinase phosphorylated the HMG-1 and 2 to a higher degree than HMG-14 and 17, the nuclear kinase exhibited a high specificity for the HMG-17, leaving the other three proteins with only a small amount. The high preference of a nuclear kinase for HMG-17 may be indicative of a specific phosphorylation occurring also in vivo.