Transcription increases multiple spontaneous point mutations in Salmonella enterica

• Published in: Nucleic acids research Vol. 31; no. 15; pp. 4517 - 4522
• Main Authors: Hudson, Richard Ellis, Bergthorsson, Ulfar, Ochman, Howard
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.08.2003; Oxford Publishing Limited (England)
• Subjects: Drug Resistance, Bacterial; Genes, Bacterial; Point Mutation; Rifampin - pharmacology; Salmonella; Salmonella enterica - drug effects; Salmonella enterica - genetics; Transcription, Genetic
• ISSN: 0305-1048; 1362-4962; 1362-4962
• DOI: 10.1093/nar/gkg651

The spontaneous rate of G·C→A·T mutations and a hotspot T·A→G·C transversion are known to increase with the frequency of transcription—increases that have been ascribed primarily to processes that affect only these specific mutations. To investigate how transcription induces other spontaneous point mutations, we tested for its effects in repair‐proficient Salmonella enterica using reversion assays of chromosomally inserted alleles. Our results indicate that transcription increases rates of all tested point mutations in the induced gene: induction significantly increased the individual rates of an A·T→T·A transversion, an A·T→G·C transition and the pooled rates of the three other point mutations assayed. Although the S.enterica genome is thought to have a mutational bias towards G·C base pairs, transitions creating A·T pairs were approximately 10 times more frequent than the reverse mutation, resulting in an overall mutation pressure to lower G+C contents. Transitions occurred at roughly twice the rate of transversions, similar to results from sequence comparisons; however, several individual transversions are more frequent than the least common transition.