Transposition of a group II intron.

Among mobile genetic elements, self-splicing introns are of particular interest. They belong to either group I or group II depending on their three-dimensional structure. Homing, the systematic intron invasion of an intronless gene when it encounters its homologous intron-bearing allele, is the only means for intron mobility so far demonstrated. It depends on the activity of the intron-encoded protein and is very specific for the acceptor site. Intron transposition, the transfer of an intron to a novel site, predicted on the basis of phylogenetic studies and in vitro reverse-splicing experiments, has been proposed to be responsible for evolutionary intron spreading. Here we present results from polymerase chain reaction experiments consistent with transposition of a group II intron. This event is proposed to account for the site-specific deletion in the mitochondrial chromosome of the fungus Podospora anserina that is associated with the premature death syndrome and might also be involved in the senescence process affecting this species.