Phagemids in cloning: Identify the statement that is NOT true for a phagemid (plasmid–filamentous phage hybrid) system.

Introduction / Context:
Phagemids are versatile vectors that combine features of plasmids and filamentous phage (such as M13). They are widely used for phage display, site-directed mutagenesis, and production of single-stranded DNA. Understanding their core genetic elements helps distinguish them from λ phage–based vectors and standard plasmids.

Given Data / Assumptions:

• Phagemids possess a plasmid ori for double-stranded replication in bacteria.
• They also include an f1 origin to enable single-stranded DNA rescue with a helper phage.
• Selectable markers (for example, ampicillin resistance) are usually present.

Concept / Approach:
The key to phagemid function is the f1 origin derived from filamentous phage, not λ. With a helper phage, phagemids can be packaged into filamentous phage particles, allowing purification of single-stranded DNA. They are not λ-based integration vectors and therefore do not require a λ att site (used by λ for site-specific integration into the E. coli chromosome).

Step-by-Step Solution:

Verification / Alternative check:
Phagemid manuals and classic vector maps (for example, pBluescript, pUC-derivatives with f1 ori) show the f1 origin and standard antibiotic markers; no λ att is present.

Why Other Options Are Wrong (i.e., they are true statements):

Common Pitfalls:
Confusing λ-based replacement/insertion vectors with filamentous phage–based phagemids; assuming all phage-related vectors need λ att sites.

Final Answer:
Phagemids routinely contain a λ att site for integration into the host chromosome.