Morse R H, Roth S Y, Simpson R T
Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Mol Cell Biol. 1992 Sep;12(9):4015-25. doi: 10.1128/mcb.12.9.4015-4025.1992.
Incorporation into a positioned nucleosome of a cis-acting element essential for replication in Saccharomyces cerevisiae disrupts the function of the element in vivo [R. T. Simpson, Nature (London) 343:387-389, 1990]. Furthermore, nucleosome positioning has been implicated in repression of transcription by RNA polymerase II in yeast cells. We have now asked whether the function of cis-acting elements essential for transcription of a gene transcribed by RNA polymerase III can be similarly affected. A tRNA gene was fused to either of two nucleosome positioning signals such that the predicted nucleosome would incorporate near its center the tRNA start site and essential A-box element. These constructs were then introduced into yeast cells on stably maintained, multicopy plasmids. Competent tRNA genes were transcribed in vivo and were not incorporated into positioned nucleosomes. Mutated, inactive tRNA genes were incorporated into nucleosomes whose positions were as predicted. This finding demonstrates that the transcriptional competence of the tRNA gene determined its ability to override a nucleosome positioning signal in vivo and establishes that a hierarchy exists between cis-acting elements and nucleosome positioning signals.
将酿酒酵母复制所必需的顺式作用元件整合到定位核小体中会破坏该元件在体内的功能[R. T. 辛普森，《自然》（伦敦）343:387 - 389，1990]。此外，核小体定位与酵母细胞中RNA聚合酶II介导的转录抑制有关。我们现在要问，RNA聚合酶III转录的基因转录所必需的顺式作用元件的功能是否会受到类似影响。一个tRNA基因与两个核小体定位信号之一融合，使得预测的核小体在其中心附近包含tRNA起始位点和必需的A框元件。然后将这些构建体导入稳定维持的多拷贝质粒上的酵母细胞中。有功能的tRNA基因在体内被转录，且未整合到定位核小体中。突变的、无活性的tRNA基因被整合到其位置如预测的核小体中。这一发现表明，tRNA基因的转录活性决定了其在体内克服核小体定位信号的能力，并确立了顺式作用元件与核小体定位信号之间存在等级关系。
