The mitochondrial genome of wild-type yeast cells: IV. Genes and spacers

Abstract

The organization of the mitochondrial genome of wild-type Saccharomyces cerevisiae cells has been investigated further, by degrading mitochondrial DNA with micrococcal nuclease. Under the conditions used, this enzyme very strongly degrades the A + T-rich stretches (spacers) whereas it only inflicts a limited number of breaks into the G + C-rich stretches (genes). The macromolecular fragments derived from the “genes” have been separated from the oligonucleotides originating from the “spacers” by gel filtration, and both sorts of products have been investigated. It has been shown (a) that the spacers are very homogeneous in base composition and have a G + C content lower than 5% (mitochondrial DNA has a G + C content of 18%); (b) that the genes are very heterogeneous in base composition, the G + C content ranging from about 25% to 50%, when the average size of the fragments is 1·2 × 10 5; smaller fragments, molecular weight 4 × 10 4, having a G + C level as high as 65%, have been isolated in a yield of 10%; the average G + C content of genes is about 32%; (c) that genes and spacers are present in about equal amounts in the mitochondrial genome and that they have comparable average sizes.