Nath K, Bollon A P
Mol Gen Genet. 1976 Aug 19;147(2):153-68. doi: 10.1007/BF00267567.
The action of Escherichia coli restriction endonuclease R1 (EcoR1) on DNA isolated from Saccharomyces cerevisiae (strain MAR-33) generates three predominent homogenously sized DNA fragments (species of 1.8, 2.2 and 2.5 kilo nucleotide base pairs (KB). Many DNA species of molecular weight greater than 2 million daltons can be recognized upon incomplete EcoR1 digestion of yeast DNA. Four additional DNA species ranging from 0.3--0.9 KB can be identified as the second major class of EcoR1-yeast DNA products. Hybridization with radioactive ribosomal RNA (rRNA) and competition with nonradioactive rRNA show that of the three predominent EcoR1-yeast DNA species, the 2.5 KB species hybridizes only with the 25S rRNA while the lighter 1.8 KB species hybridizes with the 18S rRNA. The intermediate DNA species of 2.2 KB hybridizes to a small extent with the 25S rRNA and could be a result of the presence of the 2.5 KB DNA species. The mass proportions and hybridization values of these 3 DNA species account for about 60% of the total ribosomal DNA (rDNA). The 5 Eco-R1-yeast DNA species of less than 0.9 KB (4 major and 1 minor species) hybridize to varying degrees with the 2 rRNA and can be grouped in two classes. In one class there are 3 DNA species that hybridize exclusively with the 18S rRNA. In the second class there are 2 DNA species that besides hybridizing predominently with the 25S rRNA also hybridize with the 18S rRNA. The 7 EcoR1-yeast DNA species (excluding the 2.2 KB DNA species) that hybridize with the two rRNA account for nearly a 5 million dalton DNA segment, which is very close to the anticipated gene size of rRNA precursor molecule. If the 2.2 KB DNA species is a part of the rDNA that is not transcribed or 5 sRNA then the cistron encoding the rRNA in S. cerevisiae has at least 8 EcoR1 recognition sites resulting in 8 DNA fragments upon digestion with the EcoR1. Consideration is given to the relationship of the rRNA species generated by EcoR1 digestion and the chromosomes containing ribosomal cistrons.
大肠杆菌限制性内切酶R1（EcoR1）作用于从酿酒酵母（菌株MAR - 33）中分离出的DNA，产生三个主要的大小均匀的DNA片段（1.8、2.2和2.5千个核苷酸碱基对（KB）的片段）。酵母DNA经EcoR1不完全消化后，可以识别出许多分子量大于200万道尔顿的DNA种类。另外四个范围在0.3 - 0.9 KB的DNA种类可被鉴定为EcoR1 - 酵母DNA产物的第二大类。用放射性核糖体RNA（rRNA）进行杂交以及与非放射性rRNA进行竞争实验表明，在三个主要的EcoR1 - 酵母DNA种类中，2.5 KB的种类仅与25S rRNA杂交，而较轻的1.8 KB种类与18S rRNA杂交。中间大小的2.2 KB DNA种类与25S rRNA有少量杂交，可能是由于存在2.5 KB的DNA种类所致。这三种DNA种类的质量比例和杂交值约占总核糖体DNA（rDNA）的60%。小于0.9 KB的5种Eco - R1 - 酵母DNA种类（4种主要的和1种次要的）与两种rRNA有不同程度的杂交，可分为两类。一类中有3种DNA种类仅与18S rRNA杂交。另一类中有2种DNA种类，除了主要与25S rRNA杂交外，也与18S rRNA杂交。与两种rRNA杂交的7种EcoR1 - 酵母DNA种类（不包括2.2 KB的DNA种类）占了近500万道尔顿的DNA片段，这与rRNA前体分子预期的基因大小非常接近。如果2.2 KB的DNA种类是未转录的rDNA的一部分或5 sRNA，那么酿酒酵母中编码rRNA的顺反子至少有8个EcoR1识别位点，用EcoR1消化后会产生8个DNA片段。文中还考虑了EcoR1消化产生的rRNA种类与含有核糖体顺反子的染色体之间的关系。
