Bratty J, Ferbeyre G, Molinaro C, Cedergren R
Département de biochimie, Université de Montréal, Montréal, H3C 3J7, Canada.
Curr Genet. 1996 Nov;30(5):381-8. doi: 10.1007/s002940050146.
Homologous recombination in Saccharomyces cerevisiae and other organisms can be stimulated by transcription. Consistent with this, we find that recombination of a chromosomal ade1 allele with a plasmid-borne ADE1 ORF under the control of the GAL1 promoter increased from 6.1x10(-6) to 1.7x10(-4) when transcription of the plasmid locus was induced by growing the cells in the presence of galactose. Recombination could also be stimulated by over-expressing the Gal4 transcription factor in the presence of the GAL1-ADE1 plasmid, while culturing the cells in dextrose medium. However, when transcription of the same ORF was driven from the highly active promoters of the rDNA (RNA polymerase I), and ADH1 (RNA polymerase II) genes, only background levels of recombination (5-10x10(-6)) were observed, irrespective of the carbon source. Recombination was found to involve integration of the whole plasmid and to depend on RAD51, RAD52 and RAD54. The results indicate that increased accessibility of transcriptionally active chromatin is not sufficient to cause increased rates of this kind of reciprocal exchange.
酿酒酵母及其他生物体中的同源重组可被转录所刺激。与此相符的是，我们发现，当通过在半乳糖存在的条件下培养细胞来诱导质粒位点的转录时，在GAL1启动子控制下，染色体上的ade1等位基因与质粒携带的ADE1开放阅读框之间的重组频率从6.1×10⁻⁶增加到了1.7×10⁻⁴。在存在GAL1 - ADE1质粒的情况下，通过在葡萄糖培养基中培养细胞时过表达Gal4转录因子，也可刺激重组。然而，当同一开放阅读框的转录由rDNA（RNA聚合酶I）和ADH1（RNA聚合酶II）基因的高活性启动子驱动时，无论碳源如何，仅观察到背景水平的重组（5 - 10×10⁻⁶）。发现重组涉及整个质粒的整合，并依赖于RAD51、RAD52和RAD54。结果表明，转录活性染色质可及性的增加不足以导致这种相互交换的频率增加。
