The genus Acinetobacter encompasses a heterogeneous group of bacteria that are ubiquitous in the natural environment due in part to their ability to adapt genetically to novel challenges. Acinetobacter sp. strain ADP1 (also known as strain BD413) is naturally transformable and takes up DNA from any source. Donor DNA can be integrated into the chromosome by recombination provided it possesses sufficient levels of nucleotide sequence identity to the recipient's DNA. In other bacteria, the requirement for sequence identity during recombination is partly due to the actions of the mismatch repair system, a key component of which, MutS, recognizes mismatched bases in heteroduplex DNA and, along with MutL, blocks strand exchange. We have cloned mutS from strain ADP1 and examined its roles in preventing recombination between divergent DNA and in the repair of spontaneous replication errors. Inactivation of mutS resulted in 3- to 17-fold increases in transformation efficiencies with donor sequences that were 8 to 20% divergent relative to the strain ADP1. Strains lacking MutS exhibited increased spontaneous mutation frequencies, and reversion assays demonstrated that MutS preferentially recognized transition mismatches while having little effect on the repair of transversion mismatches. Inactivation of mutS also abolished the marker-specific variations in transforming efficiency seen in mutS(+) recipients where transition and frameshift alleles transformed at eightfold lower frequencies than transversions or large deletions. Comparison of the MutS homologs from five individual Acinetobacter strains with those of other gram-negative bacteria revealed that a number of unique indels are conserved among the Acinetobacter amino acid sequences.

译文

不动杆菌属包括一群在自然环境中普遍存在的异质细菌,部分原因是它们能够在基因上适应新的挑战。不动杆菌属。ADP1菌株 (也称为BD413菌株) 是天然可转化的,并从任何来源获取DNA。只要供体DNA与受体DNA具有足够水平的核苷酸序列同一性,就可以通过重组将其整合到染色体中。在其他细菌中,重组过程中对序列同一性的要求部分是由于错配修复系统的作用,该系统的关键组成部分MutS识别异双链DNA中的错配碱基,并与MutL一起阻止链交换。我们已经从ADP1菌株中克隆了mutS,并检查了其在防止发散DNA之间的重组以及修复自发复制错误中的作用。mutS的失活导致转化效率提高3至17倍,供体序列相对于菌株adp1发散8至20% 倍。缺乏MutS的菌株表现出增加的自发突变频率,并且逆转试验表明,MutS优先识别过渡失配,而对逆转失配的修复几乎没有影响。mutS的失活还消除了在mutS () 受体中看到的特定于标记的转换效率变化,其中转换和移码等位基因的转换频率比转换或大缺失低八倍。将五个单独的不动杆菌菌株的MutS同源物与其他革兰氏阴性细菌的MutS同源物进行比较,发现不动杆菌氨基酸序列中存在许多独特的indels。

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