Changes in the physical state of DNA during the replication cycle

Abstract

According to the original hypothesis of Watson and Crick (1) each strand of the DNA double helix serves as a template for the synthesis of a new complementary strand of opposite polarity. The observations of Meselson and Stahl (2) on the replication of DNA in E. coli, as well as the in vitro studies of Kornberg and co-workers (3), have been entirely consistent with this hypothesis. However, studies with highly purified preparations of DNA polymerase have served to underscore a problem which was raised by Watson and Crick in their original formulation (1). The strands of the DNA double helix are hydrogen bonded to each other and are not free to act as templates for replication. (2) DNA in its native double helical state is not an effective template for the synthesis of new DNA by highly purified preparations of polymerase (4,5).