Subcellular location and growth stage dependence of the DNA polymerases of Euglena gracilis

The subcellular location and growth stage dependence of the DNA polymerases of Euglena gracilis strain Z and of a bleached derivative of the strain have been studied by fractionation of the enzymes from extracts of whole cells and subcellular fractions on DEAE-cellulose. A new method for the rapid isolation of nuclei was employed. Of the major enzymes, pol A has a predominantly nuclear location and pol B a predominantly cytoplasmic location. Pol A is 4-fold and pol B 15-fold more active in exponentially-growing cells than in stationary-phase cells, pol B representing 90% of the combined activities in exponential-phase cells. The activity of the mitochondrial DNA polymerase increases about 3-fold as the cells enter stationary phase while that of the chloroplast DNA polymerase is greater in exponential-phase cells. The chloroplast enzyme persists in cells which have been reversibly bleached. The results are compared to those of similar experiments involving primitive and higher eucaryotes.