Transposons and transposase — core function: In microbial genetics, the transposase gene encodes an enzyme that enables what fundamental step of transposable element movement within DNA?

Introduction / Context:
Transposable elements (transposons and insertion sequences) move within genomes and are key drivers of microbial evolution. The enzyme transposase is the workhorse of this movement. Understanding exactly what transposase does helps clarify how genes, including antibiotic resistance determinants, spread between loci and even across replicons.

Given Data / Assumptions:

• Transposase is encoded by transposable elements.
• Movement of the element requires recognition of terminal inverted repeats.
• The question contrasts transposase activity with viral replication and homologous recombination.

Concept / Approach:

Transposase binds the element’s specific DNA ends (inverted repeats) and catalyzes excision and integration into a target site. Although many transposases integrate into a broad range of target sequences, the reaction itself is a site-specific DNA cutting and joining process directed by protein–DNA recognition of defined ends rather than the long sequence homology used in general recombination.

Step-by-Step Solution:

Verification / Alternative check:

Classic Tn5/Tn10 and IS element systems demonstrate transposase-mediated cut-and-paste or replicative transposition with target site duplications, consistent with precise, enzyme-driven integration chemistry rather than homologous pairing.

Why Other Options Are Wrong:

Viral replication within a genome is mediated by integrases/replicases, not bacterial transposases.

General recombination requires RecA and long homology; transposition does not.

“None of the above” is incorrect because a correct description is provided.

Common Pitfalls:

Equating “site-specific” with “single unique site.” Transposases often have relaxed target preferences but still execute a site-specific cleavage/strand-transfer mechanism controlled by the enzyme.

Final Answer:

Site-specific integration of transposable elements