LOCALIZATION OF A CRUCIFORM CUTTING ENDONUCLEASE TO YEAST MITOCHONDRIA

We have found a cruciform cutting endonuclease in the yeast, Saccharom yces cerevisiae, which localizes to the mitochondria. This activity ap parently is associated with the mitochondrial inner membrane since the activity is not released into solution by osmolysis, in contrast to t he matrix enzyme, isocitrate dehydrogenase. The cruciform cutting acti vity appears to be encoded by CCE1. This gene has been shown to encode one of the major cruciform cutting endonucleases present in a yeast c ell. In cce1 strains, which lack CCE1 endonuclease activity, the mitoc hondrial cruciform cutting endonucleolytic activity is also absent. Si nce CCE1 is allelic to MGT1, a gene required for the highly biased tra nsmission of petite mitochondrial DNA in crosses between rho+ and hype rsuppressive rho- cells, it seems likely that the CCE1 endonuclease fu nctions within mitochondria.