transposition
Summary
Transposition is the movement of a DNA segment, a transposon, from one location in the genome to another. In bacteria it is a major mechanism for spreading antibiotic resistance genes between chromosome and plasmid and between species.
Detail
Transposons are mobile genetic elements encoding a transposase that excises and reinserts them; composite transposons carry additional cargo genes, frequently antibiotic resistance determinants, between their insertion sequences. Transposition works alongside the other mechanisms of bacterial genetic exchange: transformation, the uptake of naked environmental DNA by naturally competent organisms such as Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria; transduction, transfer by bacteriophage, which is how the toxin genes of diphtheria, botulism, cholera, and streptococcal erythrogenic toxin are disseminated; and conjugation, the plasmid-mediated transfer through a sex pilus that carries resistance plasmids and is the route by which vanA vancomycin resistance moved from enterococci to Staphylococcus aureus. Transposition explains why resistance genes hop onto conjugative plasmids and then spread widely. In a different sense the word denotes transposition of the great arteries, a cyanotic congenital heart defect from failure of the aorticopulmonary septum to spiral, producing parallel circulations that require a shunt and prostaglandin E1 until arterial switch.
Sources
- Levinson Medical Microbiology and Immunology
- First Aid for the USMLE Step 1
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