Moser D R, Moser C D, Sinn E, Campbell J L
Mol Gen Genet. 1983;192(1-2):95-100. doi: 10.1007/BF00327652.
A temperature-sensitive high copy-number mutant of plasmid NTP1, first described by Grindley et al. (1978), is lethal to bacterial cells at the non-permissive temperature. This behavior has been used to select mutations in the plasmid replication origin region that suppress the over-replication phenotype. We have identified the site of the original ts lethal mutation and the positions of the reversion mutations. The ts mutation, designated orp, for over-replication, is a single nucleotide change 23 base-pairs upstream from the transcription start site for RNA I, the repressor of plasmid replication. This change simultaneously affects the promoter for RNA I and the precursor of the primer for plasmid replication, RNA II, which is also transcribed from this region. Fusions of the mutant promoter region with the galK gene indicate that transcription is not temperature sensitive. This result suggests that the mutation affects RNA II secondary structure. The reversion mutations are also located within the RNA II coding region more than 200 bp from the site of the original ts mutation. These mutations may also affect RNA II structure.
质粒NTP1的一种温度敏感型高拷贝数突变体，最早由格林德利等人（1978年）描述，在非允许温度下对细菌细胞具有致死性。这种特性已被用于筛选质粒复制起始区域中抑制过度复制表型的突变。我们已经确定了原始温度敏感型致死突变的位点以及回复突变的位置。这个温度敏感型突变，命名为orp（过度复制之意），是在RNA I转录起始位点上游23个碱基对处的单个核苷酸变化，RNA I是质粒复制的阻遏物。这种变化同时影响RNA I的启动子和质粒复制引物RNA II的前体，RNA II也是从该区域转录的。突变启动子区域与galK基因的融合表明转录对温度不敏感。这一结果表明该突变影响RNA II的二级结构。回复突变也位于RNA II编码区域内，距离原始温度敏感型突变位点超过200 bp。这些突变也可能影响RNA II的结构。
