Conversion at large intergenic regions of mitochondrial DNA in Saccharomyces cerevisiae.

Abstract

Saccharomyces cerevisiae mitochondrial DNA deletion mutants have been used to examine whether base-biased intergenic regions of the genome influence mitochondrial biogenesis. One strain (A5.0) lacks a 5-kilobase (kb) segment extending from the proline tRNA gene to the small rRNA gene that includes oril, while a second strain (A3.7) is missing a 3.7-kb region between the genes for ATPase subunit 6 and glutamic acid tRNA that encompasses ori7 plus ori2. Growth of these strains on both fermentable and nonfermentable substrates does not differ from growth of the wild-type strain, indicating that the deletable regions of the genome do not play a direct role in the expression of mitochondrial genes. Examination of whether the 5-or 3.7-kb regions influence mitochondrial DNA transmission was undertaken by crossing strains and examining mitochondrial genotypes in zygotic colonies. In a cross between strain A5.0, harboring three active ori elements (ori2, ori3, and oriS), and strain A3.7, containing only two active oni elements (ori3 and oriS), there is a preferential recovery of the genome containing two active oni elements (37% of progeny) over that containing three active elements (20%). This unexpected result, suggesting that active oni elements do not influence transmission of respiratory-competent genomes, is interpreted to reflect a preferential conversion of the A5.0 genome to the wild type (41 % of progeny). Supporting evidence for conversion over biased transmission is shown by preferential recovery of a nonparental genome in the progeny of a heterozygous cross in which both parental molecules can be identified by size polymorphisms.

DNA Recombination-Initiation Plays a Role in the Extremely Biased Inheritance of Yeast [rho−] Mitochondrial DNA That Contains the Replication Origin ori5

“…It was reported that among 17 hypersuppressive [rho Ϫ ] mtDNA isolated, 7 had ori5, 5 had ori3, 4 had ori2, and none had ori1 (48). This may reflect the sensitivity of ori5 to the in vivo doublestranded cleavage.…”