Tanaka M, Ohmori H, Hiraga S
Mol Gen Genet. 1983;192(1-2):51-60. doi: 10.1007/BF00327646.
We have isolated E. coli mutants which can grow at 30 degrees C but not at 42 degrees C and are able to harbor the oriC plasmid (minichromosome) at a higher copy number than the parental wild-type strain at the permissive temperature. The mutants were found to contain higher amounts of chromosomal DNA per mg protein than the wild-type, whether or not they harbor the plasmid. Experimental results suggest that the higher amount of chromosomal DNA is due to a higher copy number of chromosomes and not to a larger amount of DNA per chromosome. These properties in each of the mutants are caused by a single mutation at the rpoB or rpoC gene that code for the beta or beta' subunit of RNA polymerase, respectively. The mutations are thought to affect the regulation of replication of oriC-bearing replicons, that is, the E. coli chromosome and oriC plasmids, but not the miniF plasmid.
我们分离出了大肠杆菌突变体，这些突变体能够在30摄氏度下生长，但在42摄氏度下不能生长，并且在允许温度下能够以比亲本野生型菌株更高的拷贝数携带oriC质粒（微型染色体）。无论是否携带质粒，这些突变体每毫克蛋白质中所含的染色体DNA量都比野生型高。实验结果表明，染色体DNA量的增加是由于染色体拷贝数的增加，而不是每条染色体中DNA量的增加。每个突变体的这些特性是由rpoB或rpoC基因的单个突变引起的，rpoB和rpoC基因分别编码RNA聚合酶的β或β'亚基。这些突变被认为会影响携带oriC的复制子的复制调控，即大肠杆菌染色体和oriC质粒，但不影响miniF质粒。
