Department of Life Sciences, Aalborg University, DK-9000 Aalborg, Denmark.
Plant Physiol. 2010 Dec;154(4):1831-41. doi: 10.1104/pp.110.163055. Epub 2010 Oct 12.
High mobility group (HMG) proteins of the HMGB family are chromatin-associated proteins that as architectural factors are involved in the regulation of transcription and other DNA-dependent processes. HMGB proteins are generally considered nuclear proteins, although mammalian HMGB1 can also be detected in the cytoplasm and outside of cells. Plant HMGB proteins studied so far were found exclusively in the cell nucleus. Using immunofluorescence and fluorescence microscopy of HMGB proteins fused to the green fluorescent protein, we have examined the subcellular localization of the Arabidopsis (Arabidopsis thaliana) HMGB2/3 and HMGB4 proteins, revealing that, in addition to a prominent nuclear localization, they can be detected also in the cytoplasm. The nucleocytoplasmic distribution appears to depend on the cell type. By time-lapse fluorescence microscopy, it was observed that the HMGB2 and HMGB4 proteins tagged with photoactivatable green fluorescent protein can shuttle between the nucleus and the cytoplasm, while HMGB1 remains nuclear. The balance between the basic amino-terminal and the acidic carboxyl-terminal domains flanking the central HMG box DNA-binding domain critically influences the nucleocytoplasmic distribution of the HMGB proteins. Moreover, protein kinase CK2-mediated phosphorylation of the acidic tail modulates the intranuclear distribution of HMGB2. Collectively, our results show that, in contrast to other Arabidopsis HMGB proteins such as HMGB1 and HMGB5, the HMGB2/3 and HMGB4 proteins occur preferentially in the cell nucleus, but to various extents also in the cytoplasm.
高迁移率族（HMG）蛋白是 HMGB 家族的染色质相关蛋白，作为结构因子参与转录和其他依赖于 DNA 的过程的调节。HMGB 蛋白通常被认为是核蛋白，尽管哺乳动物的 HMGB1 也可以在细胞质和细胞外检测到。迄今为止研究的植物 HMGB 蛋白仅在细胞核中发现。通过免疫荧光和与绿色荧光蛋白融合的 HMGB 蛋白的荧光显微镜检查，我们研究了拟南芥（Arabidopsis thaliana）HMGB2/3 和 HMGB4 蛋白的亚细胞定位，结果表明，除了主要的核定位外，它们还可以在细胞质中检测到。核质分布似乎取决于细胞类型。通过延时荧光显微镜观察到，用光活化绿色荧光蛋白标记的 HMGB2 和 HMGB4 蛋白可以在核和细胞质之间穿梭，而 HMGB1 保持在核内。侧翼中央 HMG 盒 DNA 结合域的碱性氨基末端和酸性羧基末端结构域之间的平衡对 HMGB 蛋白的核质分布具有关键影响。此外，蛋白激酶 CK2 介导的酸性尾部磷酸化调节 HMGB2 的核内分布。总之，我们的结果表明，与其他拟南芥 HMGB 蛋白（如 HMGB1 和 HMGB5）相比，HMGB2/3 和 HMGB4 蛋白优先存在于细胞核中，但在细胞质中的存在程度也不同。
