The relative misincorporation of G versus incorporation of A is readily visualized by the intensity of a band with slower mobility in a doublet band. The technique detected activity of Pol i in several organs of mammals, while no misGvA activity was seen in the same organs in other vertebrates in the presence of Mg2+. Inaccurate DNA synthesis due to Pol i activity was detected in human melanomas. The misGvA activity was not detected in most organs of the 129/J strain mice, which is supposed to be Pol i null. Quite unexpectedly, weak misGvA was found in the extracts of the brain of these mice when Mg2+ ions were used as a cofactor of DNA-polymerase reaction. These results could be explained in several ways. One proposal is that there is some mechanism of suppression of the nonsense mutation in the brains of 129/J mice, for example alternative splicing of the exon part with nonsense mutation. Another explanation is that the misGvA method is not 100% specific for Pol i and allows for the detection of other inaccurate Pols, for example Pol g. In the current paper we have used a novel version of the misGvA method with crude extracts of yeast cells and improved the misGvA technique for the specific detection of Pol i by inclusion of the Mn2+ ion in the reaction protocol. We examined the limitations and potential applications of the method and studied the activity of several strategic variants of Pol i schematically shown in Fig. 1A. The misGvA technology was very useful for the functional analysis of several variants of human Pol i produced in yeast. We demonstrated the pivotal role of active site D34 residue in Pol i activity, along with previously studied D126 and E127. We have found that enzyme LY2109761 company without the part encoded by exon 2 is inactive and the L62I SCH772984 change, which was proposed to have evolutionary significance, has virtually no effect on activity. We have also produced human Pol g in yeast and demonstrated that its low fidelity primer extension can be easily detected in extracts, though the pattern of bands was different from Pol i. We propose that the method could be adapted to study the fidelity of DNA replication by the extracts of yeast producing various inaccurate DNA Pols. Finally, we have found that the inaccuracy of DNA synthesis in yeast producing human DNA Pols i and g did not lead to statistically significant elevation of mutation rates in corresponding strains. Apparently, these foreign Pols are excluded from DNA transactions in live yeast cells. We used a variant of the misGvA method for the detection of Pol i in crude extracts of yeast cells.