A protein encoded by a group I intron in Aspergillus nidulans directly assists RNA splicing and is a DNA endonuclease

Some group I introns self-splice in vitro, but almost all are thought to be assisted by proteins in vivo, Mutational analysis has shown that the splicing of certain group I introns depends upon a maturase protein encoded by the intron itself, However the effect of a protein an splicing can be indirect, We now provide evidence that a mitochondrial intron-encoded protein from Aspergillus nidulans directly facilitates splicing in vitro. This demonstrates that a maturase is an RNA splicing protein, The protein-assisted reaction is as fast as that of any other known group I intron. Interestingly the protein is also a DNA endonuclease, an activity required for intron mobilization, Mobile elements frequently encode proteins that promote their propagation, Intron-encoded proteins that also assist RNA splicing would facilitate both the transposition and horizontal transmission of introns.