SELF-SPLICING ACTIVITY OF THE MITOCHONDRIAL GROUP-I INTRONS FROM ASPERGILLUS-NIDULANS AND RELATED INTRONS FROM OTHER SPECIES

The mitochondrial genome of Aspergillus nidulans contains several grou p-I introns. Each one has been assayed for its ability to self-splice in vitro in the absence of proteins. The intron from the apocytochrome b gene is unusual among subgroup IB4 introns in being able to self-sp lice, unlike a similar intron from Saccharomyces cerevisiae, The first intron in the cytochrome oxidase subunit-1 gene self-splices but only correctly completes the first step of splicing; cryptic 3' splice-sit es are recognized instead and these are also used at a low frequency i n vivo. The highly homologous intron from Podospora anserina completes both steps in vitro, The remaining introns do not self-splice, The co rrelation between subgroup category, the likely presence of specific t ertiary interactions, and self-splicing activity is discussed.