Replicator Regions of the Yeast Mitochondrial DNA Active In Vivo and in Yeast Transformants

Abstract

The replication of the mtDNA in Saccharomyces cerevisiae is independent from that of the nuclear DNA. It is continuous throughout the cell cycle (Williamson and Moustacchi 1971; Sena et al. 1975), it is active in the cdc mutants deficient for the initiation of nuclear DNA synthesis (Cottrell et al. 1973; Wintersberger et al. 1974; Newlon and Fangman 1975), and it is catalyzed by a specific mtDNA polymerase (Wintersberger and Blutsch 1976). Furthermore, in most density-labeling experiments, gradual shifts in mtDNA densities are observed (Sena et al. 1975Sena et al. 1976; Williamson and Fennell 1974). This apparent dispersive mode of replication of the mtDNA probably results from the high rate of genetic recombination between the different nonsynchronous mtDNA molecules of each yeast cell, each molecule undergoing a semiconservative replication. But the exact mechanisms of the initiation and control of yeast mtDNA replication remain poorly understood. This situation is at contrast with the precise descriptions of the process of mtDNA replication now available for some other organisms, such as the vertebrates (in this case, a distinctive D-loop mechanism with specific origins for the replication of the H and L strands has been described [Arnberg et al. 1971; Berk and Clayton 1974, 1976; Kasamatsu and Vinograd 1974; Crews et al. 1979; Martens and Clayton 1979; Nass 1980; Sekiya et al. 1980]) and the insects (in this case, the replication is initiated within the A + T-rich segment [Goddard and Wolstenholme 1980]). In the case of yeast, the difficulty in isolating intact mtDNA molecules from the...