Imura T, Toh-e A
Department of Fermentation Technology, Hiroshima University, Japan.
Agric Biol Chem. 1990 Sep;54(9):2239-46.
The Zygosaccharomyces rouxii plasmid pSB3 is one of the yeast plasmids resembling 2-microns DNA. The presence of a cis-acting locus needed for stable maintenance of pSB3 has been expected by analogy with the functions encoded by other yeast plasmids such as 2-microns DNA and pSR1. We found such a locus and designated it STB-SB3. The STB-SB3 locus was delimited within 371 bp in a unique region of pSB3. This region is included in the plasmid region where no transcript was detected. No prominent feature of the nucleotide sequence was found in this region except for a direct repeat with 65% homology consisting of 27 bp and 29 bp. This is in clear contrast with the structure of the STB locus of 2-microns DNA which has five and a half tandem repeats consisting of a highly homologous 62 bp sequence. By analyzing the sites hypersensitive to nucleases using partially purified nuclei containing pSB3, the STB-SB3 locus was found not to be tightly folded into a nucleosome structure.
鲁氏接合酵母质粒pSB3是类似于2μm DNA的酵母质粒之一。通过与其他酵母质粒（如2μm DNA和pSR1）所编码的功能进行类比，预计pSB3稳定维持所需的顺式作用位点是存在的。我们发现了这样一个位点，并将其命名为STB-SB3。STB-SB3位点在pSB3的一个独特区域内被限定在371 bp范围内。该区域包含在未检测到转录本的质粒区域内。除了由27 bp和29 bp组成的具有65%同源性的直接重复序列外，该区域未发现核苷酸序列的显著特征。这与2μm DNA的STB位点结构形成鲜明对比，后者具有由高度同源的62 bp序列组成的五个半串联重复序列。通过使用含有pSB3的部分纯化细胞核分析对核酸酶敏感的位点，发现STB-SB3位点没有紧密折叠成核小体结构。
