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Molecular and Cellular Biology, June 1999, p. 4093-4100, Vol. 19, No. 6
Centre de Génétique
Moléculaire-Centre National de la Recherche Scientifique,
91198 Gif-sur-Yvette Cedex, France
Received 18 September 1998/Returned for modification 23 November
1998/Accepted 5 March 1999
Podospora anserina is a filamentous fungus with a
limited life span. It expresses a degenerative syndrome called
senescence, which is always associated with the accumulation of
circular molecules (senDNAs) containing specific regions of the
mitochondrial chromosome. A mobile group II intron (
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Mitochondrial Group II Introns, Cytochrome
c Oxidase, and Senescence in Podospora
anserina
) has been
thought to play a prominent role in this syndrome. Intron is the
first intron of the cytochrome c oxidase subunit I gene
(COX1). Mitochondrial mutants that escape the senescence
process are missing this intron, as well as the first exon of the
COX1 gene. We describe here the first mutant of P. anserina that has the sequence precisely deleted and whose cytochrome c oxidase activity is identical to that of
wild-type cells. The integration site of the intron is slightly
modified, and this change prevents efficient homing of intron . We
show here that this mutant displays a senescence syndrome similar to that of the wild type and that its life span is increased about twofold. The introduction of a related group II intron into the mitochondrial genome of the mutant does not restore the wild-type life
span. These data clearly demonstrate that intron is not the
specific senescence factor but rather an accelerator or amplifier of
the senescence process. They emphasize the role that intron plays
in the instability of the mitochondrial chromosome and the link between
this instability and longevity. Our results strongly support the idea
that in Podospora, "immortality" can be acquired not by
the absence of intron but rather by the lack of active cytochrome
c oxidase.
*
Corresponding author. Mailing address: Centre de
Génétique Moléculaire-Centre National de la Recherche
Scientifique, 91198 Gif-sur-Yvette Cedex, France. Phone: (33) 1 69 82 38 82. Fax: (33) 1 69 82 38 77. E-mail:
sainsard{at}cgm.cnrs-gif.fr.
This work is dedicated to Leon Belcour.
Molecular and Cellular Biology, June 1999, p. 4093-4100, Vol. 19, No. 6
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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