Beier D, Stange N, Gross H J, Beier H
Institut für Biochemie, Bayerische Julius-Maximilians-Universität, Würzburg, FRG.
Mol Gen Genet. 1991 Jan;225(1):72-80. doi: 10.1007/BF00282644.
We have examined the organization of tRNA(Tyr) genes in three ecotypes of Arabidopsis thaliana, a plant with an extremely small genome of 7 x 10(7) bp. Three tRNA(Tyr) gene-containing EcoRI fragments of 1.5 kb and four fragments of 0.6, 1.7, 2.5 and 3.7 kb were cloned from A. thaliana cv. Columbia (Col-O) DNA and sequenced. All EcoRI fragments except those of 0.6 and 2.5 kb comprise an identical arrangement of two tRNA(Tyr) genes flanked by a tRNA(Ser) gene. The three tRNA genes have the same polarity and are separated by 250 and 370 bp, respectively. The tRNA(Tyr) genes encode the known cytoplasmic tRNA(G psi ATyr). Both genes contain a 12 bp long intervening sequence. Densitometric evaluation of the genomic blot reveals the presence of at least 20 copies, including a few multimers, of the 1.5 kb fragment in Col-O DNA, indicating a multiple amplification of this unit. Southern blots of EcoRI-digested DNA from the other two ecotypes, cv. Landsberg (La-O) and cv. Niederzenz (Nd-O) also show 1.5 kb units as the major hybridizing bands. Several lines of evidence support the idea of a strict tandem arrangement of this 1.5 kb unit: (i) Sequence analysis of the EcoRI inserts of 2.5 and 0.6 kb reveals the loss of an EcoRI site between 1.5 kb units and the introduction of a new EcoRI site in a 1.5 kb dimer. (ii) Complete digestion of Col-O DNA with restriction enzymes which cleave only once within the 1.5 kb unit also produces predominantly 1.5 kb fragments. (iii) Partial digestion with EcoRI shows that the 1.5 kb fragments indeed arise from the regular spacing of the restriction sites.(ABSTRACT TRUNCATED AT 250 WORDS)
我们研究了拟南芥三种生态型中tRNA（Tyr）基因的组织情况，拟南芥是一种基因组极小，仅7×10⁷ bp的植物。从拟南芥哥伦比亚生态型（Col-O）DNA中克隆出了三个含tRNA（Tyr）基因的1.5 kb EcoRI片段以及四个0.6、1.7、2.5和3.7 kb的片段，并进行了测序。除0.6和2.5 kb的片段外，所有EcoRI片段都包含两个tRNA（Tyr）基因的相同排列，两侧各有一个tRNA（Ser）基因。这三个tRNA基因具有相同的极性，分别相隔250和370 bp。tRNA（Tyr）基因编码已知的细胞质tRNA（GψATyr）。两个基因都含有一个12 bp长的间隔序列。对基因组印迹的光密度评估显示，Col-O DNA中存在至少20个拷贝的1.5 kb片段，包括一些多聚体，表明该单元存在多次扩增。来自其他两种生态型，即兰茨贝格生态型（La-O）和 Niederzenz 生态型（Nd-O）的EcoRI酶切DNA的Southern印迹也显示1.5 kb单元是主要的杂交带。几条证据支持了这个1.5 kb单元严格串联排列的观点：（i）对2.5和0.6 kb的EcoRI插入片段的序列分析显示，在1.5 kb单元之间一个EcoRI位点缺失，并且在一个1.5 kb二聚体中引入了一个新的EcoRI位点。（ii）用仅在1.5 kb单元内切割一次的限制性酶对Col-O DNA进行完全酶切，也主要产生1.5 kb的片段。（iii）用EcoRI进行部分酶切表明，1.5 kb片段确实源于限制性位点的规则间隔。（摘要截断于250字）
