Changes in the Physical State of DNA during Replication in Regenerating Liver of the Rat

Abstract
Evidence is presented which demonstrates that DNA synthesis in regenerating liver is discontinuous. In pulse-labeling experiments from 30 seconds to 10 minutes, the earliest detectable intermediate in DNA replication appears to be double-stranded DNA which has a significant degree of single-stranded character probably due to the existence of gaps in the newly synthesized strand. The label begins to move into completely double-stranded DNA 10-30 minutes after the commencement of labeling. The average molecular weight of the single-stranded "unit" of DNA replication is determined to be approximately 7.5 million. Smaller units may be produced but not observed as a result of imperfect synchronization of DNA synthesis.