Schultz C J, Coruzzi G M
New York University, Biology Department, NY 10003.
Plant J. 1995 Jan;7(1):61-75. doi: 10.1046/j.1365-313x.1995.07010061.x.
Here, a complete study is described of all the genes and isoenzymes for aspartate aminotransferase (AspAT) present in Arabidopsis thaliana. Four classes of cDNAs representing four distinct AspAT genes (ASP1-ASP4) have been cloned from Arabidopsis. Sequence analysis of the cDNAs suggests that the encoded proteins are targeted to different subcellular compartments. ASP1 encodes a mitochondrial form of AspAT, ASP3 encodes a chloroplastic/plastidic form of AspAT, whereas ASP2 and ASP4 each encode cytosolic forms of AspAT. Three distinct AspAT holoenzymes (AAT1-AAT3) were resolved by activity gel analysis. Organelle isolation reveals that AAT1 is mitochondrial-localized, AAT3 is plastid-localized, and AAT2 is cytosolic. Gene-specific Northern analysis reveals that each Asp mRNA accumulates differentially with respect to organ-type. However, the individual Asp mRNAs show no dramatic fluctuations in response to environmental stimuli such as light. Southern analysis reveals that four distinct nuclear genes probably represent the entire AspAT gene family in Arabidopsis. These molecular studies shed light on the subcellular synthesis of aspartate in Arabidopsis and suggest that some of the AspAT isoenzymes may play overlapping roles in plant nitrogen metabolism.
本文描述了对拟南芥中存在的天冬氨酸氨基转移酶（AspAT）的所有基因和同工酶的完整研究。已从拟南芥中克隆出代表四个不同AspAT基因（ASP1 - ASP4）的四类cDNA。对这些cDNA的序列分析表明，所编码的蛋白质定位于不同的亚细胞区室。ASP1编码线粒体形式的AspAT，ASP3编码叶绿体/质体形式的AspAT，而ASP2和ASP4各自编码胞质形式的AspAT。通过活性凝胶分析解析出三种不同的AspAT全酶（AAT1 - AAT3）。细胞器分离显示AAT1定位于线粒体，AAT3定位于质体，AAT2定位于胞质。基因特异性Northern分析表明，每种Asp mRNA在不同器官类型中的积累情况不同。然而，单个Asp mRNA在响应光照等环境刺激时没有明显波动。Southern分析表明，四个不同的核基因可能代表拟南芥中整个AspAT基因家族。这些分子研究揭示了拟南芥中天冬氨酸的亚细胞合成情况，并表明一些AspAT同工酶可能在植物氮代谢中发挥重叠作用。
