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从大鼠脑组织提纯高迁移率蛋白Ｉ（ＨＭＧ－Ｉ），并观察到ＨＭＧ－Ｉ在体外能被蛋白激酶Ｃ磷酸化。磷酸氨基酸分析表明，蛋白激酶Ｃ所致磷酸化反应位点是丝氨酸和苏氨酸残基。未磷酸化的ＨＭＧ－Ｉ能与ＲＣ３基因５′端上游ＤＮＡ片段结合，ＤＮＡ结合部位富含Ａ和Ｔ。经蛋白激酶Ｃ磷酸化后的ＨＭＧ－Ｉ与该片段ＤＮＡ的结合明显减弱。结果提示蛋白激酶Ｃ通过改变ＨＭｇ－Ｉ磷酸化状态影响ＨＭＧ－Ｉ的ＤＮＡ结合活性，进而有可能调节ＨＭＧ－Ｉ的生物学功能。
High-mobility protein I (HMG-I) was purified from rat brain tissue and it was observed that HMG-I was phosphorylated by protein kinase C in vitro. Phosphoric acid amino acid analysis showed that the phosphorylation reaction sites induced by protein kinase C are serine and threonine residues. Unphosphorylated HMG-I binds to the upstream 5 ’end of the RC3 gene, and DNA binding sites are rich in A and T. The binding of HMG-I phosphorylated by protein kinase C to this fragment of DNA was significantly diminished. The results suggest that protein kinase C affects the DNA-binding activity of HMG-I by altering the phosphorylation status of HMg-I, which in turn may regulate the biological function of HMG-I.