Mutational specificity of DNA precursor pool imbalances in yeast arising from deoxycytidylate deaminase deficiency or treatment with thymidylate
Disruption of the dCMP deaminase ( DCD1) gene, or provision of excess dTMP to a nucleotide-permeable strain, produced dramatic increases in the dCTP or dTTP pools, respectively, in growing cells of the yeast Saccharomyces cerevisiae. The mutation rate of the SUP4-mo gene was enhanced 2-fold by the d...
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Published in | Journal of molecular biology Vol. 220; no. 4; pp. 933 - 946 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Oxford
Elsevier Ltd
20.08.1991
Elsevier |
Subjects | |
Online Access | Get full text |
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Summary: | Disruption of the dCMP deaminase (
DCD1) gene, or provision of excess dTMP to a nucleotide-permeable strain, produced dramatic increases in the dCTP or dTTP pools, respectively, in growing cells of the yeast
Saccharomyces cerevisiae. The mutation rate of the
SUP4-mo gene was enhanced 2-fold by the dCTP imbalance and 104-fold by the dTTP imbalance. 407
SUP4-o mutations that arose under these conditions, and 334 spontaneous mutations recovered in an isogenic strain having balanced DNA precursor levels, were characterized by DNA sequencing and the resulting mutational spectra were compared. Significantly more (>;98%) of the changes resulting from nucleotide pool imbalance were single base-pair events, the majority of which could have been due to misinsertion of the nucleotides present in excess. Unexpectedly, expanding the dCTP pool did not increase the fraction of A · T → G · C transitions relative to the spontaneous value nor did enlarging the dTTP pool enhance the proportion of G · C → A · T transitions. Instead, the elevated levels of dCTP or dTTP were associated primarily with increases in the fractions of G · C → C · G or A · T → T · A transversions, respectively. Furthermore, T → C, and possibly A → C, events occurred preferentially in the
dcd1 strain at sites where dCTP was to be inserted next. C → T and A → T events were induced most often by dTMP treatment at sites where the next correct nucleotide was dTTP or dGTP (dGTP levels were also elevated by dTMP treatment). Finally, misinsertion of dCTP or dTTP did not exhibit a strand bias. Collectively, our data suggest that increased levels of dCTP and dTTP induce mutations in yeast
via nucleotide misinsertion and inhibition of proofreading but indicate that other factors must also be involved. We consider several possibilities, including potential roles for the regulation and specificity of proofreading and for mismatch correction. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 0022-2836 1089-8638 |
DOI: | 10.1016/0022-2836(91)90364-C |