A distinctive mutation spectrum associated with transcription in Saccharomyces cerevisiae.
Malcolm J. Lippert (1), Jennifer A. Freedman (2), Melissa A. Barber (1), Sue Jinks-Robertson (2)
(1) Biology Department, Saint Michael's College, 1 Winooski Park, Colchester, VT, 05439, USA;
(2) Biology Department, Emory University, 1510 Clifton Rd., Atlanta, GA 30322 USA
It previously has been demonstrated that increased transcription level stimulates spontaneous mutagenesis, a phenomenon termed Transcription-Associated Mutation (TAM). Specifically, reversion of the lys2deltaBgl frameshift allele, and forward mutation at the LYS2 locus increased 35- and 10-fold, respectively, in response to transcriptional induction from the pGal1-10 promoter. To determine the types of mutations that are associated with transcription, we obtained LYS2 forward mutation spectra under low- versus high-transcription conditions. 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 et al., 2004, Mol. Cell. Biol., in press). Currently we are developing additional reversion mutation assays that can detect specific types of transcription-associated mutations. We will present our mutation rate and spectra results. (MJL is supported by the Vermont Genetics Network through the NIH Grant Number 1 P20 RR16462 from the BRIN program of the NCRR; SJR is supported by NIH grant GM-38464.).
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