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Mol Cell Biol, May 1998, p. 2976-2985, Vol. 18, No. 5
Department of Developmental Biology, Stanford
University School of Medicine, Stanford, California 94305-5427
Received 29 December 1997/Accepted 28 January 1998
Mitochondrial DNA (mtDNA) of Saccharomyces cerevisiae
contains highly conserved sequences, called rep/ori, that
are associated with several aspects of its metabolism. These
rep/ori sequences confer the transmission
advantage exhibited by a class of deletion mutants called
hypersuppressive petite mutants. In addition, because they share
features with the mitochondrial leading-strand DNA replication origin
of mammals, rep/ori sequences have also been proposed to
participate in mtDNA replication initiation. Like the mammalian
origins, where transcription is used as a priming mechanism for DNA
synthesis, yeast rep/ori sequences contain an active
promoter. Although transcription is required for maintenance of
wild-type mtDNA in yeast, the role of the rep/ori promoter as a cis-acting element involved in the replication of
wild-type mtDNA is unclear, since mitochondrial deletion mutants need
neither transcription nor a rep/ori sequence to maintain
their genome. Similarly, transcription from the rep/ori
promoter does not seem to be necessary for biased inheritance of mtDNA.
As a step to elucidate the function of the rep/ori
promoter, we have attempted to detect transcription-dependent DNA
transactions in the mtDNA of a hypersuppressive petite mutant. We have
examined the mtDNA of the well-characterized petite mutant a-1/1R/Z1,
whose repeat unit shelters the rep/ori sequence
ori1, in strains carrying either wild-type or null alleles
of the nuclear genes encoding the mitochondrial transcription
apparatus. Complex DNA transactions were detected that take place
around GC-cluster C, an evolutionarily conserved GC-rich sequence block
immediately downstream from the rep/ori promoter. These
transactions are strictly dependent upon mitochondrial transcription.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Transcription-Dependent DNA Transactions in the Mitochondrial
Genome of a Yeast Hypersuppressive Petite Mutant
and
*
Corresponding author. Present address: Howard Hughes
Medical Institute, 4000 Jones Bridge Rd., Chevy Chase, MD
20815-6789. Phone: (301) 215-8807. Fax: (301) 215-8828. E-mail:
clayton{at}hhmi.org.
Present address: Genetic Recombination, Clare Hall Labs, Imperial
Cancer Research Fund, South Mimms, Potters Bar, Herts EN6 3LD,
England.
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