Prokaryotic cells contain two primary types of transposable elements: insertion sequences and transposons. Insertion sequences are short DNA segments that can move within the genome, facilitated by an enzyme known as transposase. This enzyme is crucial for the mobility of all transposable elements, allowing them to "jump" from one location to another. Each insertion sequence features inverted repeat sequences at both ends, which are essential for their transposition. The transposase gene is typically located between these inverted repeats, enabling its transcription and subsequent translation into the necessary protein for movement.
The second type of transposable element, transposons, are longer DNA sequences that also move around the genome. Transposons can be categorized into two types: composite transposons and simple transposons. Composite transposons are flanked by two insertion sequences, which encode transposase, while the transposon itself does not. In contrast, simple transposons are surrounded by inverted repeats and contain genes that encode for transposase, making them structurally similar to insertion sequences but generally longer.
Transposons play a significant role in the development of antibiotic resistance in bacteria, often found on plasmids known as R plasmids. This transfer of genetic material contributes to the emergence of superbugs, which are resistant to multiple drugs.
Transposons can transpose through two main mechanisms: replicative transposition and conservative transposition. Replicative transposition involves the copying of the transposon, resulting in two identical copies located in different regions of the genome, akin to a "copy and paste" method. Conversely, conservative transposition entails the transposon being excised from its original location and inserted into a new one, maintaining the same number of copies, similar to a "cut and paste" method. Understanding these mechanisms is crucial, as they have distinct implications for genetic variation and evolution within bacterial populations.
