Defective assembly of ribonucleic acid polymerase subunits in a temperature-sensitive alpha-subunit mutant of Escherichia coli.
Defective assembly of ribonucleic acid polymerase subunits in a temperature-sensitive alpha-subunit mutant of Escherichia coli.
复制标题
大肠杆菌温度敏感α亚基突变体中核糖核酸聚合酶亚基的组装有缺陷。
作者：
K. Kawakami;A. Ishihama
研究了在编码其α亚基的基因中携带突变rpoA 101或rpoA 112的温度敏感性大肠杆菌菌株的RNA聚合酶的亚基组装。在携带rpoA 112的细胞中，酶亚基的顺序组装在早期被阻断，即，改变的α亚基的二聚化或改变的α二聚体与β亚基的随后缔合。因此，未组装的游离α亚基积累，未组装的β和β '亚基迅速降解，特别是在非允许温度下。装配缺陷伴随着酶亚基的过度生产，这显然是由于参与自体调节的阻遏物全酶浓度的降低。这些结果与以前的观察结果一起[Ishihama，A.，Shimamoto，N.，Aiba，H.，Kawakami，K.，Nashimoto，H.，Tsugawa，A.，& Uchida，H.等人（1980）J. Mol. 137，137-150]表明rpoA 112突变体的温度敏感性生长归因于RNA聚合酶的组装缺陷以及组装的聚合酶的热不稳定性。相反，携带rpoA 101的突变体中改变的α亚基与野生型细胞一样有效地组装到聚合酶结构中;然而，β和β '亚基在该突变体中迅速降解。这表明突变聚合酶在结构上与代谢稳定的野生型酶不同。因此，rpoA 101突变体的ts特征是由组装的RNA聚合酶的结构和功能的改变来解释的。
The subunit assembly of RNA polymerase was investigated for the temperature-sensitive Escherichia coli strains carrying the mutation rpoA101 or rpoA112 in the gene encoding its alpha subunit, In cells carrying rpoA112, the sequential assembly of enzyme subunits is blocked at an early step, i.e., either the dimerization of altered alpha subunit or the subsequent association of altered alpha dimer with beta subunit. As a result, the unassembled free alpha subunit accumulates and the unassembled beta and beta' subunits are degraded rapidly, in particular at a nonpermissive temperature. The assembly defect is accompanied by an overproduction of enzyme subunits apparently due to the decrease in the concentration of repressor holoenzyme involved in the autogenous regulation. These results together with the previous observations [Ishihama, A., Shimamoto, N., Aiba, H., Kawakami, K., Nashimoto, H., Tsugawa, A., & Uchida, H. (1980) J. Mol. Biol. 137, 137-150] indicate that the temperature-sensitive growth of rpoA112 mutants is attributed to the assembly defect of RNA polymerase as well as to the thermolability of assembled polymerase. In contrast, the altered alpha subunit in a mutant carrying rpoA101 is assembled into the polymerase structure as efficiently as in wild-type cells; nevertheless, both beta and beta' subunits are rapidly degraded in this mutant. This indicates that the mutant polymerase is structurally different from the metabolically stable wild-type enzyme. Thus, the ts character of rpoA101 mutant is explained by the alteration in the structure and function of assembled RNA polymerase.