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首页> 外文期刊>Journal of bacteriology >Mutations of temperature sensitivity in R plasmid pSC101.
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Mutations of temperature sensitivity in R plasmid pSC101.

机译：R质粒pSC101中温度敏感性的突变。

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Temperature-sensitive (Ts) mutant plasmids isolated from tetracycline resistance R plasmid pSC101 were investigated for their segregation kinetics and deoxyribonucleic acid (DNA) replication. The results fit well with the hypothesis that multiple copies of a plasmid are distributed to daughter cells in a random fashion and are thus diluted out when a new round of plasmid DNA replication is blocked. When cells harboring type I mutant plasmids were grown at 43 degrees C in the absence of tetracycline, antibiotic-sensitive cells were segregated after a certain lag time. This lag most likely corresponds to a dilution of plasmids existing prior to the temperature shift. The synthesis of plasmid DNA in cells harboring type I mutant plasmids was almost completely blocked at 43 degrees C. It seems that these plasmids have mutations in the gene(s) necessary for plasmid DNA replication. Cells haboring a type II mutant plasmid exhibited neither segregation due to antibiotic sensitivity nor inhibition of plasmid DNA replication throughout cultivation at high temperature. It is likely that the type II mutant plasmid has a temperature-sensitive mutation in the tetracycline resistance gene. Antibiotic-sensitive cells haboring type III mutant plasmids appeared at high frequency after a certain lag time, and the plasmid DNA synthesis was partially suppressed at the nonpermissive temperature. They exhibited also a pleiotrophic phenotype, such as an increase of drug resistance level at 30 degrees C and a decrease in the number of plasmid genomes in a cell.
机译：从四环素抗性R质粒pSC101分离的温度敏感（Ts）突变质粒的分离动力学和脱氧核糖核酸（DNA）复制进行了研究。该结果与以下假设非常吻合：质粒的多个副本以随机方式分布到子细胞中，因此当新一轮质粒DNA复制被阻断时被稀释。当在不存在四环素的情况下，将携带I型突变质粒的细胞在43摄氏度下生长时，经过一定的滞后时间后，抗生素敏感性细胞就会分离。该滞后很可能对应于温度变化之前存在的质粒的稀释。携带I型突变质粒的细胞中质粒DNA的合成在43摄氏度下几乎被完全封闭。似乎这些质粒在质粒DNA复制所必需的基因中具有突变。携带II型突变质粒的细胞既不显示由于抗生素敏感性引起的分离，也不显示在高温下整个培养过程中质粒DNA复制的抑制。 II型突变质粒很可能在四环素抗性基因中具有温度敏感性突变。带有III型突变质粒的抗生素敏感性细胞经过一定的滞后时间后会高频率出现，并且质粒DNA的合成在非容许温度下被部分抑制。它们还表现出多营养型，例如在30℃下的耐药性增加和细胞中质粒基因组数目的减少。

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