Nucleoid-associated proteins (NAPs) such as IHF, HU, Fis, and H-NS alter the topology of bound DNA and may thereby affect accessibility of DNA to repair and recombination processes. To examine this possibility, we investigated the effect of IHF on the frequency of homologous recombination (HR) and point mutations in soil bacterium Pseudomonas putida by using plasmidial and chromosomal assays. We observed positive effect of IHF on the frequency of HR, whereas this effect varied depending both on the chromosomal location of the HR target and the type of plasmid used in the assay. The occurrence of point mutations in plasmid was also facilitated by IHF, whereas in the chromosome the positive effect of IHF appeared only at certain DNA sequences and/or chromosomal positions. We did not observe any significant effects of IHF on the spectrum of mutations. However, despite of the presence or absence of IHF, different mutational hot spots appeared both in plasmid and in chromosome. Additionally, the frequency of frameshift mutations in the chromosome was also strongly affected by the location of the mutational target sequence. Taking together, our results indicate that IHF facilitates the occurrence of genetic changes in P. putida, whereas the location of the target sequence affects both the IHF-dependent and IHF-independent mechanisms.

中文翻译：

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整合宿主因子IHF有助于恶臭假单胞菌的同源重组和诱变过程。

核仁相关蛋白（NAP），例如IHF，HU，Fis和H-NS会改变结合的DNA的拓扑结构，从而可能影响DNA修复和重组过程的可及性。为了检验这种可能性，我们使用质粒和染色体分析方法研究了IHF对土壤细菌恶臭假单胞菌中同源重组（HR）频率和点突变的影响。我们观察到IHF对HR频率的积极影响，而这种影响则取决于HR靶标的染色体位置和测定中所用质粒的类型。IHF还可促进质粒中点突变的发生，而在染色体中，IHF的阳性作用仅出现在某些DNA序列和/或染色体位置上。我们没有观察到IHF对突变谱的任何显着影响。然而，尽管有或没有IHF，质粒和染色体中都出现了不同的突变热点。另外，染色体中移码突变的频率也受到突变靶序列位置的强烈影响。综上所述，我们的结果表明，IHF有助于恶臭假单胞菌的遗传变化发生，而目标序列的位置会影响IHF依赖性和IHF依赖性机制。