Hirsch J, Martelo O J
Biochem J. 1978 Feb 1;169(2):355-9. doi: 10.1042/bj1690355.
A cyclic AMP-dependent nuclear protein kinase was found to be closely associated with rat liver nucleolar RNA polymerase I throughout most of its purification. This protein kinase was purified to near homogeneity. It exhibits a number of unusual catalytic properties, including the inability to utilize Mn2+ when RNA polymerase is the substrate and the ability to phosphorylate both acidic and basic substrates. Phosphorylation of RNA polymerase I by this protein kinase results in the formation of phosphoester bonds characteristic of phosphoserine and phosphothreonine. Radioautography of polyacrylamide-gel electrophoretograms of the phosphorylated RNA polymerase I revealed that the 32P was located primarily on enzyme subunits SA1, SA3, SA5, and SA6 [nomenclature of Kedinger, Gissinger & Chambon (1974) Eur. J. Biochem, 44, 421-436].
在大鼠肝脏核仁RNA聚合酶I的大部分纯化过程中，发现一种环磷酸腺苷（cAMP）依赖性核蛋白激酶与其紧密相关。这种蛋白激酶被纯化至接近均一状态。它表现出许多不同寻常的催化特性，包括以RNA聚合酶为底物时无法利用Mn2+，以及能够磷酸化酸性和碱性底物。这种蛋白激酶对RNA聚合酶I的磷酸化导致形成磷酸丝氨酸和磷酸苏氨酸特有的磷酸酯键。对磷酸化的RNA聚合酶I的聚丙烯酰胺凝胶电泳图谱进行放射自显影显示，32P主要位于酶亚基SA1、SA3、SA5和SA6上[凯丁格、吉辛热和尚邦（1974年）的命名法，《欧洲生物化学杂志》，44，421 - 436]。
