Characterization of a 3′ → 5′ exonuclease activity in the phage φ29-encoded DNA polymerase

Abstract
Purified protein p2 of phage φ29, characterized as a specific DNA polymerase involved in the initiation and elongation of φ29 DNA replication, contains a 3′ → 5′ exonuclease active on single-stranded DNA, but not on double-stranded DNA. No 5′→3′ exonuclease activity was found. The 3′→5′ exonuclease activity was shown to be associated with the DNA polymerase since 1) the two activities were heat-inactivated with identical kinetics and 2) both activities, present in purified protein p2, cosedimented in a glycerol gradient.