The Presence of an Exonuclease in Highly Purified DNA Polymerase from Bakers' Yeast

Two DNA polymerase activities from bakers' yeast can be separated by DEAE‐cellulose chromatography, one of which can be dissociated from its DNAase activity by subsequent chromatography on phosphocellulose. Both of the DEAE‐cellulose polymerases prefer nicked double‐stranded DNA and utilize single‐stranded DNA efficiently only at high ratios of enzyme to template. DNA polymerase activity is completely inhibited by p‐hydroxymercuribenzoate, suggesting that cysteine is essential for activity. The DNAase has been shown to be coincident with polymerase activity during chromatography. This enzyme hydrolyzes single‐stranded DNA preferentially, releasing deoxymononucleotides as the sole product. The rate of hydrolysis is unaffected by the presence of a 2′,3′‐dideoxy terminus on poly(dT).