Identification of a distinctive mutation spectrum associated with high levels of transcription in yeast.
High levels of transcription are associated with increased mutation rates in Saccharomyces cerevisiae, a phenomenon termed transcription-associated mutation (TAM). To obtain insight into the mechanism of TAM, we obtained LYS2 forward mutation spectra under low- versus high-transcription conditions in which LYS2 was expressed from either the low-level pLYS2 promoter or the strong pGAL1-10 promoter, respectively. Because of the large size of the LYS2 locus, forward mutations first were mapped to specific LYS2 subregions, and then those mutations that occurred within a defined 736-bp target region were sequenced. In the low-transcription strain base substitutions comprised the majority (64%) of mutations, whereas short insertion-deletion mutations predominated (56%) in the high-transcription strain. Most notably, deletions of 2 nucleotides (nt) comprised 21% of the mutations in the high-transcription strain, and these events occurred predominantly at 5'-(G/C)AAA-3' sites. No -2 events were present in the low-transcription spectrum, thus identifying 2-nt deletions as a unique mutational signature for TAM.
Lippert
Malcolm J
MJ
Department of Biology, Saint Michael's College, 1 Winooski Park, Colchester, VT 05439, USA. mlippert@smcvt.edu
Freedman
Jennifer A
JA
Barber
Melissa A
MA
Jinks-Robertson
Sue
S
D001483:Base Sequence; D002874:Chromosome Mapping; D008969:Molecular Sequence Data; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D017384:Sequence Deletion; D014158:Transcription, Genetic