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Updated: Jul 28, 2026

Direct Observation of Enzymes Replicating DNA Using a Single-molecule DNA Stretching Assay
Published on: March 24, 2010
Analysis of the Okazaki fragment distributions along single long DNAs replicated by the bacteriophage T4 proteins
P D Chastain1, A M Makhov, N G Nossal
1Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, 27599, USA.
Abstract:
Rolling circle replication from M13 DNA circles was previously reconstituted in vitro using purified factors encoded by bacteriophage T4. The products are duplex circles with linear tails >100 kb. When T4 DNA polymerase deficient in 3' to 5' exonuclease activity was employed, electron microscopy revealed short single-stranded DNA "flaps" along the replicated tails. This marked the beginning of each Okazaki fragment, allowing an analysis of the lengths of sequential Okazaki fragments on individual replicating molecules. DNAs containing runs of Okazaki fragments of similar length were found, but most showed large length variations over runs of six or more fragments reflecting the broad population distribution.
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