Mutator transposons.

Mutator (Mu) element insertion has become the main way of mutating and cloning maize genes, but we are only beginning to understand how this transposon system is regulated. Mu elements are under tight developmental control and are subject to a form of epigenetic regulation that shares some features with the regulation of paramutable maize genes. Mu-like elements (MULEs) are widespread among angiosperms, and multiple diverged functional variants appear to have coexisted in genomes for long periods. In addition to its utility, the means by which this widespread and highly mutagenic system is held in check should help us to address fundamental issues concerning the stability of genomes.