Replication analysis of mitochondrial DNA in the yeast saccharomyces cerevisae /

Abstract

The mechanisms of mitochondrial DNA (mtDNA) replication are not completely understood. The major current model of mtDNA replication involves an asynchronous, asymmetric process called D-loop replication. The D-loop model of replication requires mtTFA and RNA polymerase for initiation of replication. The nuclear gene, (RP041) encodes catalytic subunit of the RNA polymerase. Massive deletions in mtDNA (rho) can produce small mtDNA genomes that contain presumed replication origins, called ori/rep sequences or not. Those rho" genomes that have ori/rep sequences exhibit a replication/segregation advantage and are called hypersuppressive (BS rho"). Those without ori/rep sequences are called neutral, rho". All rho· mutants with deleted RP041 decrease the transcription to non-detectable levels, but mtDNA is stably maintained. This indicates that D-loop mode is not only replication mechanism found in Saccharomyces cerevisae rho" cells. Two dimensional gel electrophoresis of HS and neutral rho· mtDNA reveals evidence that another mode of replication is possibly found in these cells. The presence of long strands of single stranded mtDNA in rho· and wildtype cells grown to log phases may indicate rolling-circle mechanism of replication in Saccharomyces cerevisae cells. Mammalian cells have been found to have two modes of mtDNA replication. An asymmetric-asynchronous D-loop mechanism of mtDNA replication is found in cells that maintain their copy number of mtDNA. Another mode of mtDNA replication was identified in cells that need to reamplify the copy number of mtDNA. Analogous to these findings this study results suggests different modes of replication in cells that are rapidly increasing their mtDNA copy number (cells in log phase), possibly through a rolling circle mechanism of replication. Another mode of replication is found in stationary cells that simply maintain their mtDNA copy number, possibly by a D-loop mode of replication.