Rates Of Spontaneous Mutation

1.因为我们经常使用噬菌体T4的ri基因作为突变报告基因，所以我们对一组没有映射到经典ri基因座的类似ri的突变进行了测序，以确定它们确实映射到了哪里。一些人占据了Ri上游的基因，或者落在RIII、RIV或RV基因中，但不在其他地方。因为r基因参与了裂解抑制，这是进化学学生感兴趣的经典系统，这个结果解决了有多少基因参与的模棱两可的问题，也恰好揭示了这些基因的突变倾向中的一些异常。 2.很难测量核病毒的突变率，核病毒是人类最大的病原体类别。特别是，核病毒是否具有共同的基因组突变率的问题一直难以解决。经过多次努力，我们最近建立了一个利用在大肠杆菌上生长的噬菌体Q的模型系统。正如预期的那样，核病毒的突变率非常高，每次基因组复制约为0.04。不同类型突变的比例与大多数其他生物体中看到的有所不同，特别是转换到颠倒碱基替换的比例特别高，极少数INDELs也显示出明显的偏向单碱基插入。我们还能够测试核病毒通过冲压机过程而不是通过指数复制复制的假设，并支持冲压机假说。 3.我们先前报道了极端嗜热菌Thermus thermophilus的突变频率和种类。最近，一份报告显示，这种细菌携带4-5个基因组拷贝，这可能会影响我们的估计。我们现在已经完成了对这种情况的分析，其中描述了在多倍体、选择和其他扭曲存在的情况下计算突变率的方法，并得出结论，我们对Thermus突变率的估计没有受到显著影响。

1. Because we often use the rI gene of bacteriophage T4 as a mutation reporter, we sequenced a set of rI-like mutations that did not map at the classical rI locus in order to determine where they did map. Some occupied the gene upstream from rI, or fell in the rIII, rIV or rV genes, but not elsewhere. Because the r genes are involved in lysis inhibition, a classical system of interest to students of evolution, this result resolves ambiguities about how many genes are involved, and also happens to reveal some anomalies in the mutational propensities of those genes. 2. Mutation rates are difficult to measure in riboviruses, the largest class of human pathogens. In particular, the question of whether riboviruses share a common genomic mutation rate has resisted resolution. After many efforts, we have recently established a model system using the phage Q growing on the bacterium Escherichia coli. As expected from a ribovirus, mutation rates are very high, about 0.04 per genome replication. The ratios of different kinds of mutations are somewhat different from those seen in most other organisms, with a particularly high ratio of transition to transversion base substitutions and with very few indels also showing an apparent bias towards single-base insertions. We were also able to test the hypothesis that riboviruses replication by a stamping-machine process rather than by exponential replication, with the stamping-machine hypothesis supported. 3. We reported previously on rates and kinds of mutations in the extreme thermophile Thermus thermophilus. Recently, a report appeared suggesting that this bacterium carries 4-5 copies of its genome, which could have affected our estimates. We have now completed an analysis of this situation which describes ways to calculate mutation rates in the presence of polyploidy, selection, and other distortions, and have concluded that our estimate of the Thermus mutation rate was not significantly affected.