Rates Of Spontaneous Mutation

1.与辛辛那提大学的丹尼斯·格罗根合作，确定了在中温古生物Haloferax Volcanii中产生的自发突变的比率和种类。突变率比预测的低了几倍，而且用两种方法测量时也不同。这些突变大多是一种罕见类型的插入，即三个碱基对的倍数的添加和缺失。然后我们了解到，这个考古体保留了大约20个染色体副本，这将大大推迟突变的检测。我们怀疑这些突变大多是强显性等位基因。这是现在提交发表的一个有趣的结果，但并不是对我们假设的测试。 2.与格罗根博士合作，还确定了在真细菌嗜热菌Thermus thermophilus中发生的自发突变的比率和种类。碱基替换的突变率和比例与观察到的酸链球菌的突变频率和比例没有什么区别，这有力地支持了我们的假设。这些综合的结果还允许我们重新解释一项经典研究，得出以下结论：生命的所有三个领域都表现出相同的分子进化速度，但在原核生物中，嗜热生物的进化速度要慢得多。 3.我们以前报道过，从突变的随机分布来看，大多数突变谱包含比预期更多的具有多个突变的突变。烟草花叶病毒突变的非随机分布被模拟为两个亚群的总和，多数亚群突变频率较低，少数亚群突变频率较高。如果这一结果是普遍的，它将有助于模拟核病毒的平均突变率，结合它们在宿主内的快速进化但随着时间的推移相对基因组的稳定性。现在我们正在建立一个噬菌体系统，在这个系统中可以更有效地解决这些问题。我们还报道了在体外复制模板的DNA聚合酶分子可以产生非随机的突变爆发，这表明相当少数的聚合酶分子具有突变子表型。现在我们正在建立系统来确定这类事件的分子基础。

1. Rates and kinds of spontaneous mutations arising in the mesophilic archaeon Haloferax volcanii were determined in a collaboration with Dennis Grogan at the University of Cincinnati. The mutation rate was severalfold lower than predicted and differed when measured in two ways. The mutations were mostly indels of a rare type, additions and deletions of multiples of three base pairs. Then we learned that this archaeon maintains about 20 copies of its chromosome, which will greatly delay the detection of mutations. We suspect that the mutations were mostly strongly dominant alleles. This is an interesting result now submitted for publication, but is not a test of our hypothesis. 2. Rates and kinds of spontaneous mutations arising in the eubacterial thermophile Thermus thermophilus were also determined in collaboration with Dr. Grogan. The mutation rate and fraction of basepair substitutions were indistinguishable from those observed for S. acidocaldarius, in strong support of our hypothesis. These combined results also allow us to reinterpret a classical study to conclude that all three domains of life exhibit the same rate of molecular evolution, but that among the prokaryotes, the thermophiles evolve more slowly. 3. We reported previously that most mutational spectra contain more mutants with multiple mutations than expected from a random distribution of the mutations. The nonrandom distribution of mutations in tobacco mosaic virus has been modeled as the sum of two subpopulations, a majority with a low mutation frequency and a minority with a high mutation frequency. If this result is general, it will help to model the average mutation rate of riboviruses in combination with their rapid evolution within the host but relative genomic stability over time. Now we are establishing a phage system in which such questions can be more efficiently addressed. We also reported that DNA polymerase molecules copying a template in vitro can produce nonrandom bursts of mutations, suggesting that a substantial minority of the polymerase molecules have a mutator phenotype. Now we are establishing systems to determine the molecular basis of such events.