The rate of cytosine deamination is much higher in single-stranded DNA (ssDNA) than in double-stranded DNA, and copying the resulting uracils causes C to T mutations. To study this phenomenon, the catalytic domain of APOBEC3G (A3G-CTD), an ssDNA-specific cytosine deaminase, was expressed in an Escherichia coli strain defective in uracil repair (ung mutant), and the mutations that accumulated over thousands of generations were determined by whole-genome sequencing. C:G to T:A transitions dominated, with significantly more cytosines mutated to thymine in the lagging-strand template (LGST) than in the leading-strand template (LDST). This strand bias was present in both repair-defective and repair-proficient cells and was strongest and highly significant in cells expressing A3G-CTD. These results show that the LGST is accessible to cellular cytosine deaminating agents, explains the well-known GC skew in microbial genomes, and suggests the APOBEC3 family of mutators may target the LGST in the human genome.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Feb 23 2016|
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