TABLE 1.

Error frequencies for WT and mutant pol α in a lacZα forward mutation assay

DNA pol α	Specific activitya (%)	Plaque score		Mutation frequencyb (10−3)
		Total no. of plaques	No. of White plaques
S. cerevisiae WT	100	31,289	135	3.44
S. cerevisiae L868F	113	7,412	3,489	470
S. cerevisiae L868M	95.0	10,115	1,298	127
S. cerevisiae L868W	85.9	9,995	271	26.2
S. cerevisiae L868V	40.1	10,103	173	16.3
H. sapiens WT	100	19,561	106	4.55
H. sapiens L864F	73.0	9,219	2,748	297

^aSpecific activity of each polymerase was determined and is indicated as a value relative to that for WT pol α (Materials and Methods).

^bMutation frequencies of WT and mutant enzymes were determined by plaque color. The background frequency (0.87 × 10⁻³) for this method was subtracted for each data point.