Dubey D D, Davis L R, Greenfeder S A, Ong L Y, Zhu J G, Broach J R, Newlon C S, Huberman J A
Department of Molecular and Cellular Biology, Roswell Park Cancer Institute, Buffalo, New York 14263.
Mol Cell Biol. 1991 Oct;11(10):5346-55. doi: 10.1128/mcb.11.10.5346-5355.1991.
The silent mating-type loci of Saccharomyces cerevisiae, HML and HMR, are flanked by transcriptional silencers that have ARS activity (i.e., they function as replication origins when in plasmids). To test whether these ARS elements are chromosomal origins, we mapped origins near HML (close to the left telomere of chromosome III). Our results indicate that the HML-associated ARS elements either do not function as chromosomal replication origins or do so at a frequency below our detection level, suggesting that replication from a silencer-associated origin in each S phase is not essential for the maintenance of transcriptional repression at HML. Our results also imply that the ability of a DNA fragment to function as an ARS element in a plasmid does not ensure its ability to function as an efficient chromosomal replication origin. Telomere proximity is not responsible for inactivating these ARS elements, because they are not detectably functional as chromosomal origins even in genetically modified strains in which they are far from the telomere.
酿酒酵母的沉默交配型基因座HML和HMR两侧是具有自主复制序列（ARS）活性的转录沉默子（即当它们存在于质粒中时可作为复制起点发挥作用）。为了检测这些ARS元件是否为染色体起点，我们绘制了HML附近（靠近第三条染色体的左端粒）的起点图谱。我们的结果表明，与HML相关的ARS元件要么不作为染色体复制起点发挥作用，要么以低于我们检测水平的频率发挥作用，这表明在每个细胞周期的S期从沉默子相关起点进行复制对于维持HML处的转录抑制并非必不可少。我们的结果还表明，DNA片段在质粒中作为ARS元件发挥作用的能力并不能确保其作为高效染色体复制起点发挥作用的能力。端粒接近性并非这些ARS元件失活的原因，因为即使在经过基因改造使它们远离端粒的菌株中，它们作为染色体起点也未检测到有功能。
