The D515V substitution in human POLD1 and the analogous D520V substitution in Saccharomyces cerevisiae Pol3 severely reduce the exonuclease activity. Data with yeast D520V variant also indicates an increased rate of DNA synthesis errors in vitro.
References:
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Fazlieva, R. et al. Proofreading exonuclease activity of human DNA polymerase δ and its effects on lesion-bypass DNA synthesis. Nucleic Acids Res 37, 2854–2866 (2009). https://pubmed.ncbi.nlm.nih.gov/19282447/