DNA replication in phage P4: characterization of replicon II

Area of Science:

• Molecular Biology
• Virology
• Bacteriology

Background:

• The P4 phage is a genetic element that replicates in Escherichia coli as both a satellite phage and a plasmid.
• It possesses two overlapping replicons, replicon I and replicon II, each with specific replication requirements.
• The P4 alpha gene product, a protein with primase and helicase activities, is crucial for the replication of both replicons.

Purpose of the Study:

• To investigate the replication mechanism of replicon II in P4 phage.
• To identify the essential DNA regions and their functional roles in replicon II replication.
• To explore the interaction of host proteins with the cis-acting elements of replicon II.

Main Methods:

• Site-directed mutagenesis to identify essential replication regions.
• Electrophoretic mobility shift assays (EMSAs) to study protein-DNA interactions.
• Replication assays to assess the functional impact of mutations and DNA regions.

Main Results:

• The relative orientation of ori2 and crr sites is critical for replicon II replication.
• The ori2 region was delimited to a 22 bp sequence within the alpha gene, essential for replication.
• Mutagenesis of ori2 abolished replicon II replication, indicating its functional importance.
• EMSAs revealed specific binding of host proteins to ori1 and crr, but not to ori2, suggesting a unique replication initiation mechanism for replicon II.

Conclusions:

• Replicon II replication in P4 phage is dependent on the ori2 and crr sites, with their orientation being crucial.
• The ori2 region, located within the alpha gene, is a key cis-acting element for replicon II replication.
• Unlike ori1 and crr, ori2 does not appear to bind P4 alpha or other bacterial proteins, implying a distinct initiation mechanism.