Bacteriophage T4 proteins replicate plasmids with a preformed R loop at the T4 ori(uvsY) replication origin in vitro.

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Bacteriophage T4 DNA replication machinery is complex.
• Understanding its in vitro function aids in elucidating DNA replication mechanisms.

Purpose of the Study:

• To investigate the requirements for complete unidirectional replication of T4 origin plasmids in vitro.
• To identify essential T4 proteins and DNA elements for replication initiation and elongation.

Main Methods:

• In vitro replication assays using plasmids containing the T4 ori(uvsY) replication origin.
• Analysis of the roles of specific T4 DNA replication proteins (polymerase, clamp, loader, 32 protein, helicase, primase, 59 protein, topoisomerase).

Main Results:

• T4 replication proteins can achieve complete unidirectional plasmid replication from a preformed R loop.
• T4 DNA polymerase, clamp, loader, and 32 protein are crucial for leading-strand primer elongation.
• T4 helicase, primase, and helicase loading protein (59 protein) are essential for normal replication, with 59 protein affecting helicase-dependent replication.
• T4 DNA topoisomerase is required to prevent premature stalling of leading-strand synthesis.
• A DNA unwinding element (DUE) is essential, but its sequence can be varied.

Conclusions:

• Bacteriophage T4 replication proteins can reconstitute unidirectional plasmid replication in vitro.
• Specific T4 proteins and a DUE are critical for efficient replication initiation and elongation.
• This system provides a model for studying DNA replication initiation and fork progression.