The phosphorylation of high mobility group proteins 14 and 17 from Ehrlich ascites and L1210 invitro

The ability of the high mobility group (HMG) proteins to be phosphorylated was examined in Ehrlich ascites and L1210 cells incubated $\text{in}\text{vitro}$. HMG proteins were selectively extracted from isolated nuclei with 2% trichloroacetic acid, and electrophoretically separated on acid-urea or SDS polyacrylamide gels. Autoradiography of the gels revealed that among the HMG proteins, only HMG 14 and 17 were labeled. The specific activities of these two proteins were approximately equal to that of histone H1. Phosphorylation of HMG 14 and 17 reached a maximum in 2–3 hr and had turnover rates in pulse-chase experiments similar to that of phosphorylated histone H1.