Temperate bacteriophages: Which temperate phage lacks site specificity for chromosomal insertion and can integrate multiple copies into a single bacterial chromosome?

Introduction:Temperate bacteriophages can integrate their genomes into the host chromosome. While some use site-specific recombination, others employ transposition-like mechanisms. This question tests knowledge of a phage renowned for random integration (lack of strict site specificity) and potential for multiple insertions—features that have made it a valuable genetic tool.

Given Data / Assumptions:

• Some phages integrate at defined attachment sites (e.g., lambda at attB/attP).
• Other phages transpose into the genome with less sequence constraint.
• We are asked to pick the phage that integrates with low site specificity and can insert multiple copies.

Concept / Approach:Lambda (λ) is the model of site-specific integration via integrase at att sites. In contrast, Phage Mu (Mutator) integrates using a transposition mechanism with broad target preference, leading to diverse insertion sites and possible multicopy lysogens. Therefore, Mu matches the described behavior.

Step-by-Step Solution:Step 1: Recall λ phage: site-specific recombination at attB in the host and attP on the phage.Step 2: Recall Mu phage: transposition-based integration with low sequence specificity.Step 3: Note that Mu can integrate multiple times, creating genomic rearrangements and mutations.Step 4: Conclude Mu is the correct choice.

Verification / Alternative check:Genetics literature documents Mu as a transposable phage causing insertional mutagenesis across the chromosome. Laboratory use of Mu for mutagenesis underscores its lack of strict site specificity.

Why Other Options Are Wrong:

• Lambda enzyme integrase: an enzyme, not a phage; moreover lambda integrates site-specifically.
• Lambda DNA: relies on att sites; not random.
• Phage Mn: not a standard, recognized temperate phage in classical literature.
• P1 phage: establishes plasmid-like lysogeny; not characterized by random multicopy chromosomal insertions in the sense of Mu.

Common Pitfalls:Assuming all temperate phages integrate similarly; confusing site-specific recombination with transposition.

Final Answer:Phage Mu (Mutator phage).