Transposable Elements

Transposable elements are classified as either transposons or retrotrans-posons, depending on their mechanism of amplification. Transposons directly synthesize a DNA copy of themselves, whereas retrotransposons generate an RNA intermediate that is then reverse-transcribed (by the enzyme reverse transcriptase) back into DNA. Transposable elements fall into three major groups: DNA transposons, long terminal repeat (LTR) retrotransposons, and non-LTR retrotransposons. They also are subdivided into autonomous and nonautonomous elements, based on whether they can move independently within the genome or require other elements to perform this process, as shown in Figure 3.

DNA transposons are flanked by inverted repeats and contain two or more open reading frames (ORFs). An ORF is a DNA sequence that can be transcribed to make protein. The ORFs in DNA transposons code for the proteins required for making transposon copies and spreading them through the genome. The nonautonomous elements miniature inverted-repeat trans-posable elements (MITEs) are derived from a parent DNA transposon that nucleotides the building blocks of RNA or DNA

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