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几种基因组突变率，这些突变率是某些广泛的有机体群体的特征。(1)DNA基微生物的特征突变率约为每次基因组复制的0.003。问题是，这一比率是否也出现在包括太古猿在内的极端生物中。本文研究了在75℃、pH值3.5的条件下生长的酸性硫叶藻的诱变过程，测得的诱变率为0.002，与特征值相差不大。这种生物体中碱基对替换的比例低于所有其他以DNA为基础的生物体。(2)利用烟草花叶病毒获得了第一个核病毒突变谱，该病毒生长在携带TMV转基因的宿主中，该转基因补充了804碱基基因的缺陷，促进了病毒颗粒在细胞之间的传播。光谱中最可重塑的方面是携带多个突变的突变的高比例，远远超过基于突变频率的预测。结果表明，在病毒繁殖过程中，有时会发生不可遗传的、短暂的高度变异性。

Summary of Work: Rates of spontaneous mutation vary greatly among organisms. We have previously described several genomic mutation rates that are characteristic of certain broad groups of organisms. (1) The characteristic mutation rate for DNA-based microbes is about 0.003 per genome replication. The question arises whether this rate also occurs in extremophiles including Archeons. We have characterized the mutation process in the Archeon Sulfolobus acidocaldarius growing at pH 3.5 at 75?C. The measured rate, 0.002, is not different from the characteristic value. The proportion of base-pair substitutions in this organism is lower than in all other DNA-based organisms. (2) The first mutational spectrum for a ribovirus has been obtained using tobacco mosaic virus growing in a host carrying a TMV transgene that complements defects in the 804-base gene that facilitates the spread of virus particles between cells. The most remarakable aspect of the spectrum is the high proportion of mutants carrying multiple mutations, far in excess of predictions based on the mutant frequency. The results suggest that nonheritable, transitory hypermutability occurs from time to time during virus reproduction.