Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM 88003, USA.
Mol Genet Genomics. 2012 Dec;287(11-12):881-93. doi: 10.1007/s00438-012-0724-6. Epub 2012 Oct 19.
Glutamine synthetase (GS) catalyzes the synthesis of glutamine from glutamate and ammonia. In plants, it occurs as two major isoforms, a cytosolic form (GS(1)) and a nuclear encoded chloroplastic form. The focus of this paper is to determine the role of the 5'UTR of a GS(1) gene. GS(1) gene constructs with and without its 5' and 3' UTRs, driven by a constitutive promoter, were agroinfiltrated into tobacco leaves and the tissues were analyzed for both transgene transcript and protein accumulation. The constructs were also tested in an in vitro transcription/translation system and in Escherichia coli. Our results showed that while the 3'UTR functioned in the destabilization of the transcript, the 5'UTR acted as a translation enhancer in plant cells but not in the in vitro translation system. The 5'UTR of the GS(1) gene when placed in front of a reporter gene (uidA), showed a 20-fold increase in the level of GUS expression in agroinfiltrated leaves when compared to the same gene construct without the 5'UTR. The 5'UTR-mediated translational enhancement is probably another step in the regulation of GS in plants. The presence of the GS(1) 5'UTR in front of the GS(1) coding region allowed for its translation in E. coli suggesting the commonality of the translation initiation mechanism for this gene between plants and bacteria.
谷氨酰胺合成酶（GS）催化谷氨酸和氨合成谷氨酰胺。在植物中，它有两种主要的同工型，一种是细胞质形式（GS(1)）和一种是核编码的质体形式。本文的重点是确定 GS(1)基因 5'UTR 的作用。带有和不带有其 5'和 3'UTR 的 GS(1)基因构建体，由组成型启动子驱动，被农杆菌浸润到烟草叶片中，并对转基因转录物和蛋白积累进行了分析。这些构建体也在体外转录/翻译系统和大肠杆菌中进行了测试。我们的结果表明，虽然 3'UTR 在转录物的不稳定性中起作用，但 5'UTR 在植物细胞中作为翻译增强子起作用，但在体外翻译系统中不起作用。GS(1)基因的 5'UTR 放在报告基因（uidA）前面，与没有 5'UTR 的相同基因构建体相比，在农杆菌浸润的叶片中，GUS 表达水平提高了 20 倍。5'UTR 介导的翻译增强可能是植物中 GS 调节的另一个步骤。GS(1)编码区前面存在 GS(1)5'UTR 允许其在大肠杆菌中翻译，这表明该基因在植物和细菌之间的翻译起始机制具有共性。
