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 thei r three-dimensional structure1-3. Homing, the systematic intron invasi on of an intronless gene when it encounters its homologous intron-bear ing allele, is the only means for intron mobility so far demonstrated4 . It depends on the activity of the intron-encoded protein and is very specific for the acceptor site4-7. Intron transposition, the transfer of an intron to a novel site, predicted on the basis of phylogenetic studies8,9 and in vitro reverse-splicing experiments, has been propose d to be responsible for evolutionary intron spreading2,10-14. Here we present results from polymerase chain reaction experiments consistent with transposition of a group II intron. This event is proposed to acc ount for the site-specific deletion in the mitochondrial chromosome of the fungus Podospora anserina that is associated with the premature d eath syndrome15 and might also be involved in the senescence process16 affecting this species.