Differential phosphorylation of nuclear nonhistone high mobility group proteins HMG 14 and HMG 17 during the cell cycle.

Abstract

The phosphorylation of the high mobility group (HMG) proteins at different stages of the cell cycle was studied in synchronized HeLa [human cervical carcinoma] cells. HMG proteins were extracted and analyzed by NaDodSO4[sodium dodecyl sulfate]/polyacrylamide gel electrophoresis. Although the MW distribution of HMG remains unchanged, their total amounts increase by as much as 20-25% in the G1 and S phases when compared with amounts in G2. There was a 7-fold increase of 32P incorporation into HMG 14 in the G2 phase compared with that in G1, and a 2-fold increase of 32P incorporation into HMG 17 in early S phase relative to the incorporation in the G1 and G2 stages. HMG 1 and HMG 2 are not phosphorylated. The clear demonstration of differential phosphorylation of HMG 14 and 17 at specific stages of the cell cycle warrants a serious consideration of their role in tissue-specific maintenance of the altered chromatin structure characteristic of potentially active or actively transcribed chromatin domains.