Related Experiment Videos
Formation of a DNA loop at the replication fork generated by bacteriophage T7 replication proteins
1Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295, USA.
The Journal of Biological Chemistry
|March 28, 1998
Summary
This study visually demonstrates DNA loops at replication forks during M13 DNA replication by bacteriophage T7 proteins. These loops, formed by lagging strand displacement, confirm models of coupled DNA replication.
Area of Science:
- Molecular Biology
- Virology
- Biochemistry
Background:
- Bacteriophage T7 proteins are essential for M13 DNA replication.
- Understanding DNA replication mechanisms, including coupled leading and lagging strand synthesis, is crucial.
Purpose of the Study:
- To visualize and characterize intermediates in M13 double-stranded DNA replication by bacteriophage T7 proteins.
- To provide direct evidence for DNA loops at replication forks, as predicted by models of coupled replication.
Main Methods:
- Electron microscopy was used to examine replication intermediates.
- Biochemical labeling and synchronization experiments were performed to analyze DNA synthesis and loop formation.
Main Results:
- Replication intermediates showed a single replication fork with a linear duplex tail, associated with T7 DNA polymerase and helicase/primase.
- Fifteen to forty percent of replicating templates exhibited double-stranded DNA loops (approx. 1 kilobase) at the fork.
- Loops were composed of newly synthesized DNA and formed by lagging strand displacement, as shown by labeling and synchronization experiments.
Conclusions:
- This study provides the first direct electron microscopic evidence of DNA loops at replication forks during coupled leading and lagging strand synthesis.
- The findings support existing models of DNA replication that incorporate DNA loops to facilitate coordinated synthesis.