Jørgensen F, Kurland C G
Department of Molecular Biology, University of Uppsala, Sweden.
J Mol Biol. 1990 Oct 20;215(4):511-21. doi: 10.1016/S0022-2836(05)80164-0.
Not all ribosomes that initiate translation of an mRNA sequence will successfully complete it and produce a full-length protein product. By comparing the amounts of lacZ monomer and lacZ dimer protein expressed from a plasmid in a strictly controlled assay, we calculate a dimer to monomer ratio of 0.76. We interpret this to mean that ribosomes have a 76% chance of completing the synthesis of a beta-galactosidase polypeptide. The remaining 24% of the initiated chains end in processivity accidents. For the wild-type, premature RNA polymerase termination is found to account for roughly one-third of the processivity accidents. For the hyperaccurate SmP mutant, we observe a processivity of 0.28, but the presence of streptomycin improves this to 0.50. Thus, the hyperaccuracy with respect to missense substitutions for this mutant is accompanied by a reduced processivity. Addition of streptomycin increase the first error class and reduces the second one. This finding is relevant to the optimization of ribosome function and the growth performance of ribosome mutants.
并非所有起始翻译mRNA序列的核糖体都能成功完成翻译并产生全长蛋白质产物。通过在严格控制的实验中比较从质粒表达的lacZ单体和lacZ二聚体蛋白的量，我们计算出二聚体与单体的比例为0.76。我们将此解释为核糖体有76%的机会完成β-半乳糖苷酶多肽的合成。其余24%起始的链在持续合成过程中发生意外终止。对于野生型，发现RNA聚合酶过早终止约占持续合成意外的三分之一。对于超精确的SmP突变体，我们观察到其持续合成率为0.28，但链霉素的存在将此提高到0.50。因此，该突变体在错义替换方面的超精确性伴随着持续合成率的降低。添加链霉素增加了第一类错误并减少了第二类错误。这一发现与核糖体功能的优化以及核糖体突变体的生长性能相关。
