Fidelity of replication of repetitive DNA in mutS and repair proficient Escherichia coli
Fidelity of replication of repetitive DNA in mutS and repair proficient Escherichia coli
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DOI：
10.1016/s0027-5107(00)00169-x
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发表时间：
2001-03-01
影响因子：
2.3
通讯作者：
Cebula, TA
中科院分区：
文献类型：
--
作者：
Levy, DD;Cebula, TA
在一个物种内的菌株之间或在一个基因组内的所有遗传位点上，复制保真度并不是恒定的。复制保真度的改变可能会影响这些菌株的致病模式和进化。我们一直在研究大肠杆菌的复制保真度，包括实验室减毒菌株和食源性病原体。为了在分子水平上了解突变模式的改变，我们使用了带有tRNA突变标记基因的穿梭载体质粒，该基因已被改变为包括5、7和9对[G：C]的同源多聚体以及非重复DNA。在MutS菌株中复制该质粒会导致突变后代质粒数增加20倍。这些突变几乎都是(90%)移码突变，而碱基替换突变很少见。大多数突变是在最长的同源多聚体序列中插入或缺失一或两个[G：C]对。同样针对重复序列的较大缺失(5~70bp)也同样常见。突变随着均聚体运行的长度呈指数增加。这些突变模式，包括修复熟练菌株中出人意料的高水平，导致了对大肠杆菌K-12基因组的同源多聚体DNA的检查。这个序列基序被发现是罕见的，特别是在基因和开放阅读框架中。氨基酸同源三聚体被发现避免使用同源多聚体密码子，即使它们在大肠杆菌中的同义密码子中是首选的。在大肠杆菌基因组中，似乎存在针对串联直接核苷酸重复的主动选择，这与生物体无法准确复制这样的序列有关。爱思唯尔科学公司出版。
Replication fidelity is not constant among strains within a species or at all genetic loci within a genome. Altered fidelity of replication may affect patterns of pathogenesis and the evolution of these strains. We have been studying replication fidelity in Escherichia coli, both in laboratory attenuated strains and in food-borne pathogens. To understand the altered patterns of mutagenesis at the molecular level, we used a shuttle vector plasmid with a tRNA mutational marker gene which had been altered to include homopolymeric runs of five, seven and nine [G:C] pairs, as well as non-repetitive DNA. Replication of the plasmid in mutS strains resulted in a 20-fold increase in mutant progeny plasmids. The mutations were almost all (>90%) frameshift mutations, while base substitution mutations were rare. Most mutations were insertions or deletions of one or two [G:C] pairs in the longest homopolymeric runs. Larger deletions (5 to >70 bp), also targeted to the repetitive sequence, were likewise common. Mutations increased exponentially with the length of the homopolymeric run. These patterns of mutation, including unexpectedly high levels in repair proficient strains, led to an examination of the E. coli K-12 genome for homopolymeric DNA. This sequence motif was found to be rare, particularly in genes and open reading frames. Amino acid homotrimers were found to avoid usage of homopolymeric codons, even when they are preferred among synonymous codons in E. coli. There appears to be active selection against tandem direct nucleotide repeats in the E. coli genome, correlated with the inability of the organism to accurately replicate such sequence. Published by Elsevier Science B.V.