Tuned for Transposition: Molecular Determinants Underlying the Hyperactivity of a Stowaway MITE

MITE-y Jumps Tranposable elements are genetic elements ubiquitous to most genomes, and their expansion, loss, and potential movement are major components of genome evolution. A type of noncoding transposable element in plants, known as a MITE (minature inverted repeat transposable element), shows evidence of recent expansion within specific rice genomes. However, these elements lack the necessary transposase to help them move. Yang et al. (p. 1391 ; see the Perspective by González and Petrov ) found that the expansion of MITEs occurs because they exploit the activity of other, unrelated, transposons and consequently identified the molecular determinants that allowed mobilization. Surprisingly, the element coding for the transposase repressed its own movement unless the MITE was present. These findings may explain why some genetic elements can replicate within the genome and reach high copy numbers while others do not.