Taylor S S
J Biol Chem. 1982 Jun 10;257(11):6056-63.
When a mixture of DNA-free core histones (H) from calf thymus is phosphorylated by the catalytic subunit of cAMP-dependent protein kinase, phosphate is incorporated primarily into H2B and, to a lesser extent, into H3 and H4. In contrast, when the phosphorylation of the DNA-free histones is compared to the phosphorylation of histones in long chromatin or in nucleosome core, only one of the core histones, H3, is phosphorylated. The site of modification of H3 has been identified as serine 10, which is located in the highly charged basic NH2-terminal region of the molecule. The other sites of phosphorylation in H2B nd H4 are completely masked when the histones are complexed with DNA. It is only when the nucleosome core structure is perturbed that these additional sites become accessible to the kinase. If long chromatin which contains H1 is phosphorylated, histone 1 is also phosphorylated by catalytic subunit at serine 38. However, the addition of excess H1 to H1-depleted long chromatin inhibits the phosphorylation of H3. In addition to the histones, the high mobility group (HMG) protein, HMG 14, was also found to be a good substrate for the kinase. Phosphorylation of HMG 17 in comparison was much less.
当来自小牛胸腺的无DNA核心组蛋白（H）混合物被环磷酸腺苷依赖性蛋白激酶的催化亚基磷酸化时，磷酸主要掺入H2B，其次少量掺入H3和H4。相比之下，当将无DNA组蛋白的磷酸化与长染色质或核小体核心中组蛋白的磷酸化进行比较时，只有一种核心组蛋白H3被磷酸化。H3的修饰位点已被确定为丝氨酸10，它位于分子带高电荷的碱性NH2末端区域。当组蛋白与DNA复合时，H2B和H4中的其他磷酸化位点被完全掩盖。只有当核小体核心结构受到干扰时，这些额外的位点才能被激酶识别。如果含有H1的长染色质被磷酸化，组蛋白H1也会在丝氨酸38处被催化亚基磷酸化。然而，向H1缺失的长染色质中添加过量的H1会抑制H3的磷酸化。除了组蛋白外，高迁移率族（HMG）蛋白HMG 14也被发现是该激酶的良好底物。相比之下，HMG 17的磷酸化程度要低得多。
