Zhao Jing, Paul Laju K, Grafi Gideon
Department of Plant Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel.
Biochim Biophys Acta. 2009 Nov-Dec;1789(11-12):751-7. doi: 10.1016/j.bbagrm.2009.09.004. Epub 2009 Sep 23.
The high mobility group (HMG) proteins are nonhistone chromosomal proteins that participate in diverse nuclear activities including chromatin structure and gene regulation. We previously studied the biochemistry of the maize HMGA protein and its role in transcriptional regulation during maize endosperm development. Here, we extended our study and showed that a strong binding of ZmHMGA to AT-rich DNA requires at least three AT-hook motifs; two motifs showed a significant reduction whereas a single motif was not sufficient for binding. CDK phosphorylation sites situated between AT-hook3 and AT-hook4 were strongly phosphorylated by a SUC1-associated kinase; no in vitro phosphorylation is evident for the AtHMGA protein. Phosphorylation of ZmHMGA reduced its binding to AT-rich DNA in vitro. The maize HMGA protein fused to GFP was localized in the nucleus of transgenic Arabidopsis plants tending to concentrate within the nucleolus. Localization to the nucleolus was conferred by the C-terminal portion of the protein containing the AT-hooks. ZmHMGA was acetylated in vitro on its N-terminal globular domain by the human PCAF acetyltransferase. Our results suggest that ZmHMGA participates in nucleolar function and that its role may be regulated posttranslationally by phosphorylation and acetylation.
高迁移率族（HMG）蛋白是非组蛋白染色体蛋白，参与多种核活动，包括染色质结构和基因调控。我们之前研究了玉米HMGA蛋白的生物化学及其在玉米胚乳发育过程中转录调控中的作用。在此，我们扩展了研究，结果表明ZmHMGA与富含AT的DNA的强结合至少需要三个AT钩基序；两个基序的结合显著减少，而单个基序不足以实现结合。位于AT钩3和AT钩4之间的细胞周期蛋白依赖性激酶（CDK）磷酸化位点被一种与SUC1相关的激酶强烈磷酸化；AtHMGA蛋白在体外没有明显的磷酸化现象。ZmHMGA的磷酸化在体外降低了其与富含AT的DNA的结合。与绿色荧光蛋白（GFP）融合的玉米HMGA蛋白定位于转基因拟南芥植物的细胞核中，倾向于集中在核仁内。蛋白的含AT钩的C末端部分赋予了其核仁定位特性。ZmHMGA在体外其N末端球状结构域被人PCAF乙酰转移酶乙酰化。我们的结果表明ZmHMGA参与核仁功能，并且其作用可能在翻译后通过磷酸化和乙酰化进行调控。
