THE YEAST MITOCHONDRIAL INTRON AI5-ALPHA - ASSOCIATED ENDONUCLEASE ACTIVITY AND INVIVO MOBILITY

By analyzing crosses between yeast strains carrying different combinations of mitochondrial (mt) introns, we have shown that the aI5-alpha intron is mobile in vivo. Furthermore, we have observed that the mobility of intron aI5-alpha is affected by both the nuclear and mt genotypes. We have also detected a restriction endonuclease (ENase) activity that cleaves intronless mt genomes close to the aI5-alpha intron insertion site and thus might be involved in intron mobility. This is further supported by the fact that this ENase activity is only detected in a strain containing the aI5-alpha intron. Furthermore, similar to other ENases encoded by mobile mt introns of yeast, the ENase generates a cut with a four-base 3'-OH overhang. Thus, intron aI5-alpha represents a characteristic member of the family of mobile group-I introns.