Analysis of Mutagenesis in the Escherichia coli tdk Gene: The Nucleoid Protein HNS Is Required for a Dramatic Cisplatin‐Induced Hotspot

We demonstrate the utility of the tdk reporter gene system, by showing its ability to not only analyze mutational hotspots, but also to allow the analysis of both weak and strong mutator or mutagen effects. It can detect large and small insertions and deletions, as well as base substitutions. We previously defined cisplatin (CPT)-induced hotspots in tdk. One extraordinary hotspot for G:C- > T:A transversions at base pair (bp) 499 is in a region of the gene that appears to be mutationally prone, suggesting that the conformation of the DNA in that region may play a major role in elevating mutation rates. Here, we examined CPT-induced mutations in a derivative of the starting wild-type strain that lacks the nucleoid binding protein HNS, which is involved in the folding and compaction of the E. coli chromosome. In this strain background the extraordinary CPT-induced hotspot disappears, pinpointing the importance of DNA conformation in mutation rates at certain positions. We further show that this A:T-rich gene is a magnet for transposable elements.