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，所以我们对一组未在经典rI基因座上作图的rI样突变进行了测序，以确定它们在哪里作图。有些占据了rI基因上游，或落在rIII、rIV或rV基因中，但不在其他地方。因为r基因参与了溶解抑制，这是进化论学生感兴趣的一个经典系统，这个结果解决了关于有多少基因参与的模糊不清的问题，也恰好揭示了这些基因突变倾向的一些异常。 2.核糖病毒是人类病原体中最大的一类，其突变率很难测量。特别是，核糖病毒是否具有共同的基因组突变率的问题一直难以解决。经过许多努力，我们最近建立了一个模型系统，使用噬菌体Q生长在细菌大肠杆菌。正如从核糖体病毒所预期的那样，突变率非常高，每个基因组复制约0.04。不同类型的突变的比例与大多数其他生物体中所见的有些不同，其中转换到颠换碱基取代的比例特别高，并且很少有indel也显示出对单碱基插入的明显偏好。我们也能够测试的假设，即核糖病毒复制的冲压机过程，而不是指数复制，冲压机假说的支持。 3.我们以前报道过极端嗜热栖热菌的突变率和突变种类。最近，一份报告显示，这种细菌携带4-5个基因组拷贝，这可能影响了我们的估计。我们现在已经完成了对这种情况的分析，描述了在存在多倍性、选择和其他扭曲的情况下计算突变率的方法，并得出结论，我们对栖热菌突变率的估计没有受到显着影响。

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.