MACRONUCLEAR DNA OF HYPOTRICHOUS CILIATE OXYTRICHA-FALLAX
MACRONUCLEAR DNA OF HYPOTRICHOUS CILIATE OXYTRICHA-FALLAX
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DOI：
10.1073/pnas.75.10.4992
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发表时间：
1978-01-01
影响因子：
11.1
通讯作者：
SPEAR, BB
中科院分区：
文献类型：
--
作者：
RAE, PMM;SPEAR, BB
与其他低毛纤毛虫原生动物一样，黄花棘豆大核中的DNA以小的无染色体分子形式存在，而不是在染色体中。本文报道了用物理化学方法和核酸杂交技术对黄花菜DNA的研究。大核DNA分子的大小从22千碱基对(Kb)到约0.5kb不等。脱氧核糖核酸在氯化铯中的浮力密度为1.694克碳纳米点。Cm-3，熔融温度为15 mM氯化钠/1.5 mM柠檬酸钠，pH为7，温度为65.4℃。这两个值分别对应34.7%的GUA+Cyt和28.1%的GUA+Cyt，TLC测得碱基组成为32.4%的GUA+Cyt。唯一能检测到的修饰核苷酸是N6-甲基脱氧腺苷(0.2%)，修饰的数量和种类不能解释3种方法测定核苷酸组成的差异。25S和19S rRNA基因包含在长度为6.67kb的DNA分子中，其中至少有6.15kb被转录。这些rDNA分子不像其他一些低等真核生物中的rDNA那样显示出链内互补，并且它们有两个不对称位点被内切酶EcoRI识别。5S RNA的基因位于DNA分子中，长度为0.69kb。用限制性内切酶BamHI、BsuI、Hhai和Taqi对这段DNA进行消化，没有证据表明存在随机重复的序列。Oxytricha大核中的19S+25S rRNA基因和5S rRNA基因很可能都是以单个转录单位的形式存在，并且都可能有大约0.5kb的间隔区。
DNA in the macronuclei of O. fallax, as in other hypotrichous ciliate protozoa, exists as small, achromosomal molecules rather than in chromosomes. Studies on O. fallax DNA using physicochemical procedures and nucleic acid hybridization are reported. Macronuclear DNA molecules range in size from 22 kilobase pairs (kb) to about 0.5 kb. The DNA has a buoyant density in CsCl of 1.694 g .cntdot. cm-3 and a melting temperature in 15 mM NaCl/1.5 mM sodium citrate, pH 7, at 65.4.degree.. These values correspond to 34.7% Gua + Cyt and 28.1% Gua + Cyt, respectively, and base composition determined by TLC of nucleotides is 32.4% Gua + Cyt. The only modified nucleotide detectable is N6-methyldeoxyadenylate (0.2%), and the amount and kind of modification cannot account for the discrepancies in nucleotide composition determination by the 3 methods. The genes for 25S and 19S rRNA are contained in DNA molecules 6.67 kb in length, of which at least 6.15 kb is transcribed. These rDNA molecules show no intrastrand complementarity as does rDNA in some other lower eukaryotes, and they have 2 asymmetric sites recognized by endonuclease EcoRI. The genes for 5S RNA are in DNA molecules 0.69 kb in length. Digestion of this DNA with restriction enzymes BamHI, BsuI, HhaI, and TaqI gives no evidence for a tandemly repeated sequence. It is likely that both 19S + 25S rRNA genes and 5S RNA genes in the Oxytricha macronucleus exist as single transcription units, and both may have spacer regions approximately 0.5 kb long.