Replication and Maintenance of Linear Phage-Plasmid N15

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The lambdoid phage N15 of Escherichia coli exhibits unique biology, existing as a linear plasmid prophage rather than integrating into the host chromosome.
• This linear plasmid possesses covalently closed ends (telomeres) and utilizes a specialized tyrosine recombinase family enzyme, protelomerase, for its unique life cycle.

Purpose of the Study:

• To elucidate the mechanisms underlying the stable inheritance and replication of the N15 linear plasmid prophage.
• To investigate the role of protelomerase and the unique centromere structure in N15 phage biology.

Main Methods:

• Analysis of N15 phage DNA structure and replication intermediates.
• Identification and characterization of the protelomerase enzyme and its activity.
• Investigation of the N15 partitioning operon and centromere function.

Main Results:

• N15 prophage replication initiates internally, producing duplicated telomeres resolved by protelomerase, yielding multiple linear plasmid molecules.
• The N15 centromere comprises four dispersed inverted repeats, crucial for efficient partitioning, unlike the single centromere of the F factor.
• Partition protein binding to centromeric sites regulates phage replication and lytic development.

Conclusions:

• The N15 phage represents a distinct class of temperate phages with a linear plasmid prophage, relying on protelomerase and dispersed centromeres for propagation.
• N15-like phages, including those from marine gamma-proteobacteria, share conserved genetic elements, suggesting a common evolutionary origin.