SOS Induction by Stabilized Topoisomerase IA Cleavage Complex occurs via the RecBCD pathway

Abstract

Enzymes known as topoisomerases regulate the topology of DNA. Antibacterial drugs such as quinolones target type II topoisomerase by trapping the cleavage complex formed between the enzyme and cleaved DNA. This subsequently leads to accumulated double stranded breaks that result in bacterial cell death. Due to increasing resistance to these antibacterial drugs, it is essential to identify new drug targets. One such target is topoisomerase IA, which cleaves a single strand of DNA. The overall purpose of this study is to investigate the cellular response to stabilized type IA DNA topoisomerase cleavage complex in Escherichia coli. A mutant of the Yersinia pestis topoisomerase IA has been shown to form a stabilized cleavage complex resulting in SOS induction and extensive bacterial cell death. This topoisomerase mutant was used to determine whether the RecBCD or RecFOR enzyme complexes were involved in SOS induction and the repair of this stabilized cleavage complex. The study concluded that RecBCD was required to induce the SOS response in E. coli cells expressing the recombinant mutant topoisomerase and for repair of the topoisomerase cleavage complex. This suggests that the single‐stranded break associated with the topoisomerase IA cleavage complex is first converted to a double‐stranded break for repair by the RecBCD enzyme and subsequent induction of the SOS response and homologous recombination.