Whole genome annotation of an Escherichia coli isolate reveals a small mobile element approximately 800 bp long, bounded by perfect inverted repeats and encoding a single open reading frame homologous to transposase. How should this element be classified?
- A Insertion sequence element ✓
- B Composite transposon carrying resistance genes between two IS elements
- C Integron with a gene cassette array
- D Conjugative transposon of the Tn916 family
Correct answer: A. Insertion sequence element
Explanation
An insertion sequence is the simplest transposable element: roughly 700 to 1500 bp, flanked by short inverted repeats, and encoding only the transposase needed for its own movement. B composite transposon is distinguished by having additional passenger genes, usually antimicrobial resistance determinants, lying between two IS modules, so it is much larger. Integrons lack terminal inverted repeats with transposase and capture gene cassettes instead, and Tn916 family elements are large conjugative units measured in tens of kilobases.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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