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Replication of polyoma DNA in isolated nuclei: analysis of replication fork movement
Abstract:
The movement of replication forks during polyoma DNA synthesis in isolated nuclei was analyzed by digesting newly synthesized DNA with the restriction endonuclease HpaII which cleaves polyoma DNA into eight unique fragments. The terminus of in vitro DNA synthesis was identified by cleaving newly completed molecules with HpaII. The distribution of label in the restriction fragments showed that the in vitro DNA synthesis was bidirectional and had the normal terminus of replication. Analysis of replicative intermediates pulse-labeled in vitro further suggested that DNA synthesis in isolated nuclei is an ordered process similar to replication in intact cells. Replication forks moved with a constant rate from the origin towards the terminus of replication. The nonlinear course of the DNA synthesis reaction in the isolated nuclei seems to result from the random inactivation of replication forks rather than a decrease in the rate of fork movement. During the in vitro synthesis a replication fork could maximally synthesize a DNA chain about 1,000 nucleotides long. The results suggest that some replication forks might be initiated in vitro at the origin of replication.
Insights
Polyoma DNA replication in isolated nuclei is bidirectional, with replication forks moving at a constant rate. Fork inactivation, not slowing, explains the reaction
Area of Science:
- Molecular Biology
- Virology
- Biochemistry
Background:
- Understanding DNA replication mechanisms is crucial for cell biology and disease research.
- Polyoma virus DNA replication provides a model system for studying eukaryotic DNA synthesis.
- In vitro systems allow detailed analysis of replication processes under controlled conditions.
Purpose of the Study:
- To analyze the movement and characteristics of replication forks during polyoma DNA synthesis in isolated nuclei.
- To determine if in vitro DNA synthesis in isolated nuclei mimics replication in intact cells.
- To investigate factors influencing the rate and progression of DNA replication forks.
Main Methods:
- Newly synthesized polyoma DNA in isolated nuclei was digested with the restriction endonuclease HpaII.
- HpaII cleaves polyoma DNA into eight unique fragments, allowing analysis of labeled DNA distribution.
- Replicative intermediates were pulse-labeled in vitro to study the ordered process of DNA synthesis.
Main Results:
- In vitro DNA synthesis was confirmed to be bidirectional with a normal replication terminus.
- Replication forks moved at a constant rate from origin to terminus.
- Nonlinear DNA synthesis resulted from random replication fork inactivation, not decreased fork speed; forks synthesized up to 1,000 nucleotides.
Conclusions:
- DNA synthesis in isolated nuclei is an ordered process, mirroring replication in intact cells.
- Replication fork inactivation is the primary cause of reaction nonlinearity in this in vitro system.
- Initiation of some replication forks in vitro at the origin of replication is suggested.