RFLP and physical mapping with an rDNA-specific endonuclease reveals that nucleolus organizer regions of Arabidopsis thaliana adjoin the telomeres on chromosomes 2 and 4
RFLP and physical mapping with an rDNA-specific endonuclease reveals that nucleolus organizer regions of Arabidopsis thaliana adjoin the telomeres on chromosomes 2 and 4
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DOI：
10.1046/j.1365-313x.1996.09020259.x
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发表时间：
1996-02-01
期刊：
影响因子：
7.2
通讯作者：
Pikaard, CS
中科院分区：
文献类型：
--
作者：
Copenhaver, GP;Pikaard, CS
核糖体RNA基因以称为核仁组织区（NORs）的串联阵列组织。在之前的一项研究中，脉冲场凝胶上的RFLP定位将NOR2定位在拟南芥2号染色体的北端。新的多态性使得另一个NOR， NOR4，被定位到4号染色体的北端。在绒泡菌中，一种具有15个核苷酸识别序列的内切酶I- ppol参与了一个可移动的、自剪接的I组内含子的rdna归巢。拟南芥基因组DNA的I-Ppol酶切释放出两个不大于13 kbp的端粒片段，并利用I-Ppol与NOR2和NOR4共分离鉴定出端粒多态性。限制性位图显示，端粒-近端rRNA基因的5′端最靠近染色体末端，3′端最靠近着丝粒。通过克隆端粒- rdna连接的聚合酶链反应证实了这个方向，很可能是4号染色体上的连接。端粒重复序列连接末端rRNA基因下游的启动子，表明第一个基因是无活性的。亚端粒重复dna在端粒- rdna连接处缺失。NOR2、NOR4及其相关端粒TEL2N和TEL4N的定位为2号染色体和4号染色体的遗传和物理图谱提供了终点。
Ribosomal RNA genes are organized in tandem arrays called nucleolus organizer regions (NORs). In a prior study, RFLP mapping on pulsed-field gels placed NOR2 at the northern tip of Arabidopsis thaliana chromosome 2. New polymorphisms have allowed the other NOR, NOR4, to be mapped to the northern tip of chromosome 4. To map NOR-associated loci, rDNA-specific cleavage by I-Ppol, an endonuclease with a 15 nucleotide recognition sequence involved in rDNA-homing of a mobile, self-splicing Group I intron in Physarum was exploited. I-Ppol digestion of A. thaliana genomic DNA liberated two telomere-containing fragments no larger than 13 kbp, and telomere polymorphisms identified using I-Ppol cosegregated with NOR2 and NOR4. Restriction mapping suggested that telomere-proximal rRNA genes are oriented with their 5' ends nearest the chromosome ends and their 3' ends nearest the centromere. This orientation was confirmed using the polymerase chain reaction to clone one of the telomere-rDNA junctions, most likely the junction on chromosome 4. The telomeric repeats join the terminal rRNA gene downstream of its promoter, suggesting that this first gene is inactive. Subtelomeric repetitive DNAs are absent at the telomere-rDNA junction. Localization of NOR2, NOR4 and their associated telomeres, TEL2N and TEL4N, respectively, provides end points for the genetic and physical maps of chromosomes 2 and 4.