MUTATIONAL SPECIFICITY OF THE DNAE173 MUTATOR ASSOCIATED WITH A DEFECT IN THE CATALYTIC SUBUNIT OF DNA POLYMERASE-III OF ESCHERICHIA-COLI
MUTATIONAL SPECIFICITY OF THE DNAE173 MUTATOR ASSOCIATED WITH A DEFECT IN THE CATALYTIC SUBUNIT OF DNA POLYMERASE-III OF ESCHERICHIA-COLI
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DOI：
10.1016/0022-2836(91)90586-u
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发表时间：
1991-12-20
影响因子：
5.6
通讯作者：
SEKIGUCHI, M
中科院分区：
文献类型：
--
作者：
MO, JY;MAKI, H;SEKIGUCHI, M
我们开发了一种系统来检测发生在多拷贝质粒上的大肠埃希菌L基因的正向突变。利用该体系，我们确定了DNA聚合酶III编辑功能受阻的adna E173突变株的突变特异性。对突变株中87个独立的L−突变进行了测序分析，并以从dna E+菌株中回收的10 0个突变株为对照，对突变株的L−突变频率进行了分析。虽然野生型菌株中发生的突变数量的一半是由插入元件引起的，但从突变菌株中没有恢复到这样的突变。在dna E173菌株中发现了一种新的突变类型，命名为“序列替换”；突变株中诱导的7个序列替换发生在6个位点，并且都位于准回文序列中，在一个或两个端点携带GTG或CAC序列。虽然在两个菌株中都发现了其他类型的突变，但单碱基移码是突变菌株中最常见的事件。因此，这类突变的突变子效应是175,000倍。突变株中95%的单碱基移码是附加的，其中大部分发生在A或C碱基的游程，以增加相同残基的数量。碱基替换主要发生在突变子菌株的几个热点上，而在野生型菌株中诱导的碱基替换更随机地分布在整个L序列中，其频率因突变效应而增加了25,000倍。Dna E173突变子还使复制频率增加了28,000倍。在从突变株中恢复的三个复制中，一个是简单复制，其区域两侧有直接重复。其他复制是复杂的，其中一半位于包含两组反向重复序列的区域的反向方向。从野生型菌株中也发现了相同的复制。目前的数据表明，dna E173是一类新的突变子，它能迅速地诱导序列定向突变，产生高频率的单碱基移位、重复与倒置、序列替换和热点碱基替换。
We developed a system to examine forward mutations that occurred in therpsLgene ofEscherichia coliplaced on a multicopy plasmid. Using this system we determined the mutational specificity for adnaE173mutator strain in which the editing function of DNA polymerase III is impeded. The frequency ofrpsL−mutations increased 32,000-fold, due to thednaE173mutator, and 87 independentrpsL−mutations in the mutator strain were analyzed by DNA sequencing, together with 100 mutants recovered fromdnaE+strain, as the control. While half the number of mutations that occurred in the wild-type strain were caused by insertion elements, no such mutations were recovered from the mutator strain. A novel class of mutation, named “sequence substitution” was present in mutants raised in thednaE173strain; seven sequence substitutions induced in the mutator strain occurred at six sites, and all were located in quasipalindromic sequences, carrying the GTG or CAC sequence at one or both endpoints. While other types of mutation were found in both strains, single-base frameshifts were the most frequent events in the mutator strain. Thus, the mutator effect on this class of mutation was 175,000-fold. A total of 95% of the single-base frameshifts in the mutator strain were additions, most of which occurred at runs of A or C bases so as to increase the number of identical residues. Base substitutions, the frequency of which was enhanced 25,000-fold by the mutator effect, occurred primarily at several hotspots in the mutator strain, whereas those induced in the wild-type strain were more randomly distributed throughout therpsLsequence. ThednaE173mutator also increased the frequency of duplications 28,000-fold. Of the three duplications recovered from the mutator strain, one was a simple duplication, the region of which was flanked by direct repeats. The other duplications were complex, one half part of which was in the inverted orientation of a region containing two sets of inverted repeats. The same duplications were also recovered from the wild-type strain. The present data suggest thatdnaE173is a novel class of mutator that sharply induces sequence-directed mutagenesis, yielding high frequencies of single base frameshifts, duplications with inversions, sequence substitutions and base substitutions at hotspots.