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

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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.