Module 3.2: Transposition Mechanisms & Control

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Test 1 (3.2) — Transposition Mechanisms & Control

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3.2 Transposition Mechanisms & Control — Test 1

Q1. Bacteriophage Mu is notable because it:✓ Uses transposition as its mechanism of replication and integration

Q2. Phage Mu replicates its genome during the lytic cycle mainly by:✓ Replicative transposition

Q3. The Tn3 element controls its own transposition frequency through:✓ Resolvase (TnpR) acting as a repressor of the transposase gene

Q4. Tn10 down-regulates its own transposition using:✓ Antisense RNA (RNA-OUT pairing with RNA-IN) that blocks transposase translation

Q5. Tn10 transposition is also influenced by Dam methylation, which:✓ Couples transposition to passage of the replication fork (hemimethylated state activates it)

Q6. Multicopy inhibition of Tn10 means that:✓ Increasing element copy number decreases transposition per element (via antisense RNA)

Q7. In Mu transposition, the transposase is encoded by gene:✓ MuA

Q8. The accessory protein MuB functions to:✓ Deliver/capture target DNA and stimulate strand transfer (ATP-dependent)

Q9. 'Transposition immunity' (target immunity) ensures that:✓ A transposon avoids inserting into a DNA molecule that already contains a copy

Q10. Replicative transposition (e.g. Tn3, Mu) proceeds through a key intermediate called the:✓ Cointegrate

Q11. DDE transposases (like MuA) are named for:✓ A catalytic triad of two aspartates and a glutamate that coordinates Mg²⁺

Q12. Cut-and-paste transposases create a hairpin or double-strand break by:✓ Cleaving both strands at the transposon ends to excise the element

Q13. After cut-and-paste excision of Tn10, the donor site is:✓ Left with a double-strand break that the host must repair

Q14. The heat-shock response in E. coli that can influence stress-related gene expression uses the regulator:✓ σ³² (σH, RpoH) sigma factor

Q15. Why is tight regulation of transposition advantageous for the host-element relationship?✓ Excessive transposition would damage the host genome, harming both host and element survival

Q16. Strand transfer in transposition refers to:✓ Joining of the transposon 3'-OH ends to the target DNA

Q17. Phage Mu integrates into the host genome at:✓ Essentially random target sites (hence its mutagenic nature)

Q18. A key difference between replicative and conservative transposition is that replicative transposition:✓ Increases element copy number (one copy stays, one is made at the target)

Q19. Antisense RNA control of Tn10 (RNA-OUT) works by:✓ Base-pairing with the transposase mRNA to occlude its ribosome-binding site

Q20. In the Tn3 family, the control logic is best described as:✓ tnpA + tnpR, where TnpR represses transposase and resolves cointegrates