Nuclear Targeting of Methyl-Recycling Enzymes in Arabidopsis thaliana Is Mediated by Specific Protein Interactions  

作　　者：Sanghyun Lee Andrew C. Doxey Brendan J. McConkey Barbara A. Moffatt 

机构地区：[1]Department of Biology, University of Waterloo, Waterloo, ON, N2L 3G1, Canada [2]Department of Developmental Biology, Stanford University, Stanford, CA 94305, USA

出　　处：《Molecular Plant》2012年第1期231-248,共18页分子植物（英文版）

摘　　要：Numerous transmethylation reactions are required for normal plant growth and development. S-adenosylhomocysteine hydrolase （SAHH） and adenosine kinase （ADK） act coordinately to recycle the by-product of these reactions, S-adenosylhomocysteine （SAH） that would otherwise competitively inhibit methyltransferase （MT） activities. Here, we report on investigations to understand how the SAH produced in the nucleus is metabolized by SAHH and ADK. Localization analyses using green fluorescent fusion proteins demonstrated that both enzymes are capable of localizing to the cytoplasm and the nucleus, although no obvious nuclear localization signal was found in their sequences. Deletion analysis revealed that a 41-amino-acid segment of SAHH （GlylS^-Lys19~） is required for nuclear targeting of this enzyme. This segment is surface exposed, shows unique sequence conservation patterns in plant SAHHs, and possesses additional features of protein-protein interaction motifs. ADK and SAHH interact in Arabidopsb via this segment and also interact with an mRNA cap MT. We propose that the targeting of this complex is directed by the nuclear localization signal of the MT; other MTs may similarly target SAHH/ADK to other subcellular compartments to ensure uninterrupted transmethylation.Numerous transmethylation reactions are required for normal plant growth and development. S-adenosylhomocysteine hydrolase （SAHH） and adenosine kinase （ADK） act coordinately to recycle the by-product of these reactions, S-adenosylhomocysteine （SAH） that would otherwise competitively inhibit methyltransferase （MT） activities. Here, we report on investigations to understand how the SAH produced in the nucleus is metabolized by SAHH and ADK. Localization analyses using green fluorescent fusion proteins demonstrated that both enzymes are capable of localizing to the cytoplasm and the nucleus, although no obvious nuclear localization signal was found in their sequences. Deletion analysis revealed that a 41-amino-acid segment of SAHH （GlylS^-Lys19~） is required for nuclear targeting of this enzyme. This segment is surface exposed, shows unique sequence conservation patterns in plant SAHHs, and possesses additional features of protein-protein interaction motifs. ADK and SAHH interact in Arabidopsb via this segment and also interact with an mRNA cap MT. We propose that the targeting of this complex is directed by the nuclear localization signal of the MT; other MTs may similarly target SAHH/ADK to other subcellular compartments to ensure uninterrupted transmethylation.

关 键 词：TRANSMETHYLATION subcellular localization S-adenosylhomocysteine hydrolase adenosine kinase nuclear targeting protein docking protein modeling protein motif analysis. 

分 类 号：Q51[生物学—生物化学] Q783.1