PT  - JOURNAL ARTICLE
AU  - Amit Bachar
AU  - Elad Itzhaki
AU  - Shmuel Gleizer
AU  - Melina Shamshoom
AU  - Ron Milo
AU  - Niv Antonovsky
TI  - Point mutations in topoisomerase I alter the mutation spectrum in <em>E. coli</em> and impact the emergence of drug resistance genotypes
AID  - 10.1101/621045
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 621045
4099  - http://biorxiv.org/content/early/2019/04/28/621045.short
4100  - http://biorxiv.org/content/early/2019/04/28/621045.full
AB  - Identifying the molecular mechanisms that give rise to genetic variation is essential for the understanding of evolutionary processes. Previously, we have used adaptive laboratory evolution to enable biomass synthesis from CO2 in E. coli. Genetic analysis of adapted clones from two independently evolving populations revealed distinct enrichment for insertion and deletion mutational events. Here, we follow these observations to show that mutations in the gene encoding for DNA Topoisomerase 1 (topA) give rise to mutator phenotypes with characteristic mutational spectra. Using genetic assays and mutation accumulation lines, we show that point mutations in topA increase the rate of sequence deletion and duplication events. Interestingly, we observe that a single residue substitution (R168C) results in a high rate of head-to-tail (tandem) short sequence duplications, which are independent of existing sequence repeats. Finally, we show that the unique mutation spectrum of topA mutants enhances the emergence of antibiotic resistance in comparison to mismatch-repair (mutS) mutators, and lead to new resistance genotypes. Our findings highlight a potential link between the catalytic activity of topoisomerases and the fundamental question regarding the emergence of de novo tandem repeats, which are known modulators of bacterial evolution.