Influence of ethidium bromide on respiration in Schizosaccharomyces pombe

Ethidium bromide rejuvenation of senescent cultures of Podospora anserina : Loss of senescence-specific DNA and recovery of normal mitochondrial DNA

The effect of ethidium bromide (EB) which is known to be able to "rejuvenate" senescent mycelia in Podospora anserina, has been investigated at the level of the mitochondrial DNA (mtDNA) by restriction analysis and molecular hybridization. While senescent mycelia display a very low growth ability and gross mtDNA modifications (tandem amplification of short sequences and disorganization of the mitochondrial chromosome: deletion of large sequences), the rejuvenated mycelia display a normal life span and contain a mtDNA in all respects identical to that of wild type mycelium (neither circular molecules nor amplified fragments could be detected). These results demonstrate a strict correlation between the senescent state and the presence of amplified mtDNA and suggest that EB rejuvenation could proceed by an efficient selection of intact mitochondrial chromosomes still present in senescent cultures.

A cytoplasmic gene for partial suppression of a nuclear pleiotropic respiratory deficient mutant in the petite negative yeast Schizosaccharomyces pombe

The nuclear pleiotropic respiratory-deficient mutant pet1 (previously M126) exhibits cytochromes aa3 and b deficiencies accompanied by loss of the oligomycin-sensitivity of the mitochondrial ATPase. The mutant pet1, unable to grow on glycerol, growth on glucose. The latter phenotypic trait symbolized by ANAS-D, exhibits a high frequency (2 to 4 X 10(5)) Of spontaneous suppression into Antimycin A-resistant strains. Mutagenesis with MnCl2 increases by a factor of 10(2) the frequency of ANAR-D derivatives. This suppression is partial since none of the suppressed strains is able to grow on glycerol even when respiratory functions and cytochromes activities are restored as in the pet1 [SUP2] strain. In the latter strain it is concluded that the extralocus suppressor gene [SUP2] is responsible for the ANAR-D trait. Tetrad analysis in a cross homozygous for pet1 demonstrates a non-Mendelian segregation pattern for the SUP2 suppressor gene. In stable diploids, homozygous for pet1, the [SUP2] suppressor exhibits a mitotic segregation pattern. Furthermore the transmission of the [SUP2] gene is decreased by ethidium bromide treatment. Therefore, the [SUP2] suppressor gene responsible for partial suppression of the nuclear pleiotropic phenotype in mutant pet1 is of cytoplasmic heredity.