title: The mitochondrial nucleoid protein, Mgm101p, of Saccharomyces cerevisiae is involved in the maintenance of rho(+) and ori/rep-devoid petite genomes but is not required for hypersuppressive rho(-) mtDNA.
abstract: The Saccharomyces cerevisiae MGM101 gene encodes a DNA-binding protein targeted to mitochondrial nucleoids. MGM101 is essential for maintenance of a functional rho(+) genome because meiotic segregants, with a disrupted mgm101 allele, cannot undergo more than 10 divisions on glycerol medium. Quantitative analysis of mtDNA copy number in a rho(+) strain carrying a temperature-sensitive allele, mgm101-1, revealed that the amount of mtDNA is halved each cell division upon a shift to the restrictive temperature. These data suggest that mtDNA replication is rapidly blocked in cells lacking MGM101. However, a small proportion of meiotic segregants, disrupted in MGM101, have rho(-) genomes that are stably maintained. Interestingly, all surviving rho(-) mtDNAs contain an ori/rep sequence. Disruption of MGM101 in hypersuppressive (HS) strains does not have a significant effect on the propagation of HS rho(-) mtDNA. However, in petites lacking an ori/rep, disruption of MGM101 leads to either a complete loss or a dramatically decreased stability of mtDNA. This discriminatory effect of MGM101 suggests that replication of rho(+) and ori/rep-devoid rho(-) mtDNAs is carried out by the same process. By contrast, the persistence of ori/rep-containing mtDNA in HS petites lacking MGM101 identifies a distinct replication pathway. The alternative mtDNA replication mechanism provided by ori/rep is independent of mitochondrial RNA polymerase encoded by RPO41 as a HS rho(-) genome is stably maintained in a mgm101, rpo41 double mutant.
authors.affiliation: Molecular Genetics and Evolution Group, Research School of Biological Sciences, The Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Xiao Ming
authors.initials: XM
authors.lastname: Zuo
authors.forename: G Desmond
authors.initials: GD
authors.lastname: Clark-Walker
authors.forename: Xin Jie
authors.initials: XJ
authors.lastname: Chen
mesh_terms: D004261:DNA Replication; D004272:DNA, Mitochondrial / Q000096:biosynthesis*; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000502:physiology*; D006358:Hot Temperature; D008928:Mitochondria / Q000235:genetics; D024101:Mitochondrial Proteins; D009154:Mutation; D009687:Nuclear Proteins / Q000502:physiology*; D018741:Replication Origin; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology*
chemical_list: D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C082519:MGM101 protein, S cerevisiae; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins