Related Experiment Videos
Multiple origins and circular structures in replicating T5 bacteriophage DNA
Abstract:
Replicating T5 phage DNA was gently isolated using NaI density gradient centrifugation and examined by electron microscopy. At the beginning of phage DNA synthesis, linear unit-length T5 DNA molecules containing from one to four replicating "eye-loops" were consistently observed. Replication in these molecules was found to proceed bidirectionally from multiple, internal origins. A primary origin of replication is located near the center of the T5 genome, which does not coincide with the location of any of the nicks (single-strand breaks) found in mature T5 DNA. The initiation of replication at the various origins within an individual molecule does not appear to follow any definite temporal sequence. At later times in the infection, we have observed a significant number of circular T5 DNA molecules-both replicating and nonreplicating-whose average circumference is approximately the length of mature T5 DNA minus the terminal redundancy. The replicating circular molecules appear to be either in a theta configuration, a sigma configuration with the tails all being less than the length of the circle, or a combination of theta and sigma forms.
Insights
Replication of T5 phage DNA initiates bidirectionally from multiple internal origins. Both linear and circular DNA molecules exhibit complex replication patterns, including theta and sigma forms, indicating a dynamic process.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- T5 phage DNA replication is a complex process.
- Understanding replication origins is crucial for viral DNA synthesis.
Purpose of the Study:
- To investigate the origins and patterns of T5 phage DNA replication.
- To characterize the structures of replicating T5 DNA molecules.
Main Methods:
- Gentle isolation of T5 phage DNA using NaI density gradient centrifugation.
- Examination of DNA molecules via electron microscopy.
Main Results:
- Early replication shows linear T5 DNA with multiple "eye-loops" originating bidirectionally from internal sites.
- A primary origin is near the T5 genome center, not at nicks.
- Later stages reveal circular T5 DNA (replicating and non-replicating) and various replication intermediates (theta, sigma forms).
Conclusions:
- T5 phage DNA replication initiates from multiple internal origins.
- Replication proceeds bidirectionally, with complex intermediate structures observed.
- Circularization of DNA occurs during later stages of replication.