Unternährer S, Pridmore D, Hinnen A
Ciba-Ciba-Geigy AG, Biotechnology Department, Basel, Switzerland.
Mol Microbiol. 1991 Jun;5(6):1539-48. doi: 10.1111/j.1365-2958.1991.tb00801.x.
The yeast 2 microns plasmid is found in the nucleus of almost all Saccharomyces cerevisiae strains. Its replication is very similar to that of chromosomal DNA. Although the plasmid does not encode essential genes it is stably maintained in the yeast population and exhibits only a small, though detectable, loss rate. This stability is achieved by a plasmid-encoded copy-number control system which ensures constant plasmid levels. For the investigation of 2 microns replication, a yeast strain that is absolutely dependent on this plasmid was constructed. This was achieved by disruption of the chromosomal CDC9 gene, coding for DNA ligase and providing this essential gene on a 2 microns-derived plasmid. This plasmid is absolutely stable under all growth conditions tested. Using the temperature-sensitive mutant allele cdc9-1 we have developed an artificial control system which allows one to change the copy number of 2 microns-derived plasmids solely by changing the incubation temperature.
酵母2微米质粒存在于几乎所有酿酒酵母菌株的细胞核中。其复制过程与染色体DNA的复制非常相似。虽然该质粒不编码必需基因，但它在酵母群体中能稳定维持，且丢失率很低，不过仍可检测到。这种稳定性是通过质粒编码的拷贝数控制系统实现的，该系统可确保质粒水平恒定。为了研究2微米质粒的复制，构建了一种绝对依赖该质粒的酵母菌株。这是通过破坏编码DNA连接酶的染色体CDC9基因，并在源自2微米质粒的载体上提供这个必需基因来实现的。在所有测试的生长条件下，该质粒都绝对稳定。利用温度敏感突变等位基因cdc9-1，我们开发了一种人工控制系统，该系统允许仅通过改变培养温度来改变源自2微米质粒的拷贝数。
