Rates Of Spontaneous Mutation

工作总结：不同生物体的自发突变率差异很大。我们之前已经描述了基因组突变率，这是某些广泛的有机体群体的特征。核病毒每次复制的基因组突变率为0.1？1，接近生存所需的最大值。核病毒(烟草花叶病毒)的第一个突变谱显示，携带多个突变的突变比例很高，远远超过基于突变频率和随机分布的突变的预测。基于脱氧核糖核酸的微生物的特征突变率约为每次基因组复制的0.003。在生长在75摄氏度的朱砂中，突变率接近0.003，但碱基对替换的比例低于所有其他以dna为基础的生物。我们假设，平均错义突变在高温下具有更大的有害影响。因此，进化压力会降低碱基替换突变率。这一假说的一个预测是，在进化过程中积累的错义突变与沉默(同义)突变的比率，在嗜热者中将低于中嗜热者。另一种预测是，嗜热真细菌也会表现出碱基对替换的频率降低，但中温古细菌不会。

Summary of Work: Rates of spontaneous mutation vary greatly among organisms. We have previously described genomic mutation rates that are characteristic of certain broad groups of organisms. Riboviruses have genomic mutation rates of 0.1?1 per replication, a value approaching the maximum compatible with survival. The first mutational spectrum for a ribovirus (tobacco mosaic virus) displayed a high proportion of mutants carrying multiple mutations, far in excess of predictions based on the mutant frequency and randomly distributed mutations. The characteristic mutation rate for DNA-based microbes is about 0.003 per genome replication. In the Archeon Sulfolobus acidocaldarius growing at 75 degrees C, the mutation rate is close to 0.003 but the proportion of base-pair substitutions is lower than in all other DNA-based organisms. We hypothesized that the average missense mutation has a greater deleterious effect at high temperatures. As a result, evolutionary pressures would act to decrease base-substitution mutation rates. One prediction of this hypothesis is that the ratio of missense to silent (synonymous) mutations accumulating in the course of evolution would be lower in thermophiles than in mesophiles. Another prediction is that a thermophilic eubacterium would also show reduced frequencies of base-pair substitutions but that a mesophilic archaeon would not.