In vitro replication directed by a cloned adenovirus origin

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Adenovirus DNA replication is a complex process.
• Understanding the origins and mechanisms of viral DNA replication is crucial for virology.
• Recombinant DNA technology allows for the study of specific viral DNA fragments.

Purpose of the Study:

• To investigate the replication of type 2 adenovirus DNA using a recombinant plasmid.
• To identify and characterize the origin of adenovirus DNA replication.
• To elucidate the mechanism of adenovirus DNA replication, including the directionality and strand displacement.

Main Methods:

• Construction of a recombinant plasmid (XD-7) containing the left terminal XbaI-E fragment of type 2 adenovirus.
• In vitro replication assays using nuclear and cytoplasmic extracts from infected and uninfected HeLa cells.
• Electron microscopy to map the replication origin and analyze replication intermediates.
• Site-directed mutagenesis (deletion and orientation reversal) to assess the role of the identified origin.

Main Results:

• Recombinant plasmid XD-7 replicated as rolling circles in extracts from adenovirus-infected cells, forming single-stranded tails.
• The adenovirus origin of replication was mapped to the left boundary of the cloned adenovirus DNA segment.
• Replication proceeded rightwards, indicating displacement of the viral l strand.
• Reversing the origin's orientation altered replication direction, and deletion abolished replication, confirming its essential role.

Conclusions:

• The identified left-end fragment contains the functional origin of type 2 adenovirus DNA replication.
• Adenovirus DNA replication initiates at this origin and proceeds via a strand displacement mechanism.
• The pBR322 vector sequences do not contain a functional origin of replication for this process.