Functional Modulation of the Geminivirus AL2 Transcription Factor and Silencing Suppressor by Self-Interaction
Functional Modulation of the Geminivirus AL2 Transcription Factor and Silencing Suppressor by Self-Interaction
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DOI：
10.1128/jvi.00617-07
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发表时间：
2007-08
影响因子：
5.4
通讯作者：
Xiaojuan Yang;Surendranath Baliji;R. Buchmann;Hui Wang;J. Lindbo;G. Sunter;D. Bisaro
中科院分区：
文献类型：
--
作者：
Xiaojuan Yang;Surendranath Baliji;R. Buchmann;Hui Wang;J. Lindbo;G. Sunter;D. Bisaro
摘要双生病毒的DNA基因组具有有限的编码能力，这种能力通过产生小的多功能蛋白质来补偿。由菜豆病毒属（Begomovirus）成员编码的AL 2蛋白（例如，番茄金色花叶病毒（Tomato golden mosaic virus）是一种转录激活因子、沉默抑制因子和基础防御抑制因子。甜菜曲顶病毒（Curtovirus属）的相关蛋白L2具有AL 2的致病功能，但缺乏转录激活活性。已知AL2和L2可以通过与腺苷激酶（ADK）相互作用来抑制局部沉默，并且可以通过与SNF1激酶相互作用来抑制基础防御。然而，这些病毒蛋白的活性是如何调节的仍然是一个未解之谜。在这里，我们通过证明AL2而不是L2与自身相互作用来提供一些答案。锌指样基序（CCHC）是必需的，但不足以使AL2自身相互作用。丙氨酸取代不变的半胱氨酸残基，包括基序取消自我相互作用或导致异常的亚核定位，但不取消与ADK和SNF1的相互作用。使用双分子荧光互补，我们表明，AL 2：AL 2复合物主要积累在细胞核中，而AL 2：ADK和L2：ADK复合物主要积累在细胞质中。此外，半胱氨酸残基突变损害了AL2激活外壳蛋白启动子的能力，但不影响局部沉默抑制。因此，AL2自身相互作用与核定位和转录的有效激活相关，而AL2和L2单体可以通过与细胞质中的ADK相互作用来抑制局部沉默。
ABSTRACT The DNA genomes of geminiviruses have a limited coding capacity that is compensated for by the production of small multifunctional proteins. The AL2 protein encoded by members of the genus Begomovirus (e.g., Tomato golden mosaic virus) is a transcriptional activator, a silencing suppressor, and a suppressor of a basal defense. The related L2 protein of Beet curly top virus (genus Curtovirus) shares the pathogenicity functions of AL2 but lacks transcriptional activation activity. It is known that AL2 and L2 can suppress local silencing by interacting with adenosine kinase (ADK) and can suppress basal defense by interacting with SNF1 kinase. However, how the activities of these viral proteins are regulated remains an unanswered question. Here, we provide some answers by demonstrating that AL2, but not L2, interacts with itself. The zinc finger-like motif (CCHC) is required but is not sufficient for AL2 self-interaction. Alanine substitutions for the invariant cysteine residues that comprise the motif abolish self-interaction or cause aberrant subnuclear localization but do not abolish interaction with ADK and SNF1. Using bimolecular fluorescence complementation, we show that AL2:AL2 complexes accumulate primarily in the nucleus, whereas AL2:ADK and L2:ADK complexes accumulate mainly in the cytoplasm. Further, the cysteine residue mutations impair the ability of AL2 to activate the coat protein promoter but do not affect local silencing suppression. Thus, AL2 self-interaction correlates with nuclear localization and efficient activation of transcription, whereas AL2 and L2 monomers can suppress local silencing by interacting with ADK in the cytoplasm.