Supersuppressive "petite" mutants of yeast.

A class of suppressive "petite" mutants of S. cerevisiae, called here supersuppressive, is characterized by a) the fact that their unmodified mitochondrial genomes are the only ones found in the progeny of crosses with wild-type cells; b) very short repeat units (400-900 base pairs) in their mitochondrial genomes. The repeat units of the three supersuppressive "petites" investigated here share a common 83 nucleotide sequence, which seems to correspond to an initiation site of DNA replication; the multiple copies of this site in the mitochondrial genomes of supersuppressive "petites" might explain why these genomes can compete out those of wild-type cells.