Function of a short spacer between rice EPSP synthase and rps20 genes.

我们将具有水稻愈伤组织中表达的序列的片段定位到水稻蜡质基因座周围328-kb BAC重叠群的物理图谱上。在杂交片段中，我们试图表征位于蜡质下游约45 kb区域的强杂交片段。发现这些片段含有编码5-烯醇式莽草酸-3-磷酸合酶（EPSPs）和核糖体蛋白小亚基20（rps 20）的两个管家基因。有趣的是，这些管家基因是相邻的，只有一个303 bp的间隔区，并在尾对尾方向的指导。通过对愈伤组织cDNA文库的筛选，获得了这两个基因的近全长cDNA克隆。EPSPs基因的克隆具有一个1683 bp的开放阅读框架，编码一个推导的561个氨基酸（aa）的多肽，这是第一个表达的基因在水稻中使用这种方法确定。EPSPs是莽草酸合成途径中的关键酶，定位于高等植物的质体中。已知这种酶是 关于我们 草甘膦是一种非选择性除草剂。水稻rps 20肽的基因先前已被分离，我们的rps 20 cDNA克隆完全匹配该肽的注册序列。使用从粳稻和籼稻品系的根、幼苗、小穗和花药中提取的总RNA进行北方印迹分析。EPSPs基因的2.2kb转录本在根、幼苗和小穗的RNA样品中很容易检测到，但在花药的RNA样品中检测不到。一个0.75 kb的rps 20转录检测在所有组织中，我们检查，虽然在两个水稻株系的根中的表达是非常弱的。我们已经检查了任一基因的转录本的程度。这些转录物在间隔区之外进行;另一个基因的表达可能被来自相反基因的反义RNA修饰，产生双链RNA，这可能在称为转录后基因沉默的机制中作为RNA降解的触发器。这里发现的短间隔区在高等植物的核基因组织中是不常见的。该片段可能与植物核基因组中间隔区的扩展或收缩有关，并可能在相反基因转录引起的基因调控中发挥作用。少

We mapped the fragments with sequence (s) expressed in the rice callus onto a physical map for a 328-kb BAC contig around the rice waxy locus. Among the hybridized fragments, we attempted to characterize strongly hybridized fragments located in a region about 45 kb downstream of waxy. The fragments were found to contain two housekeeping genes encoding 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) and ribosomal protein small subunit 20 (rps20). Interestingly, these housekeeping genes are adjoined, with only a 303-bp spacer, and are directed in a tail-to-tail orientation. Nearly-full-length cDNA clones of the two genes were obtained by screening the callus cDNA library. A clone for the EPSPs gene possessed an open reading frame of 1683 bp encoding a deduced 561-amino-acid (aa) polypeptide that is the first expressed gene identified in rice using this method. EPSPs is a key enzynae on the shikimate pathway and is localized in the plastids of higher plants. This enzyme is known to be … More targeted by glyphosate, which has been employed as a nonselective herbicide. A gene for the rice rps20 peptide had previously been isolated, and our rps2O cDNA clone completely matched the registered sequence for this peptide. Northern blotting analyses were conducted using blots of total RNAs extracted from roots, seedlings, spikelets and anthers of Japonica and Indica rice strains. The 2.2-kb transcript of the EPSPs gene was easily detected in RNA samples from roots, seedlings and spikelets, but not the RNA from anthers. A 0.75-kb rps20 transcript was detected in all the tissues we examined, although the expression in roots from both rice strains was very weak. We have examined an extent of the transcript of either gene. These transcripts proceeded beyond the spacer ; the expression of the other gene might be modified by the antisense RNA from the opposite gene, resulting in double-stranded RNA, which might act as a trigger for RNA degradation in the mechanism called post-transcriptional gene silencing. The short spacer found here is uncommon in the nuclear gene organization in higher plants. This segment may have evolutionary implications about spacer expansion or contraction in the plant nuclear genome, and may play a role in gene regulation caused by the opposite gene transcript. Less