Open AccessThe Mitochondrial Nucleoid Protein, Mgm101p, of Saccharomyces cerevisiae Is Involved in the Maintenance of ρ+ and ori/rep-Devoid Petite Genomes but Is Not Required for Hypersuppressive ρ− mtDNA
Author(s) -
Xiao Ming Zuo,
G. D. Clark-Walker,
Xin Jie Chen
Publication year - 2002
Publication title -
genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.792
H-Index - 246
eISSN - 1943-2631
pISSN - 0016-6731
DOI - 10.1093/genetics/160.4.1389
Subject(s) - biology , mitochondrial dna , genetics , genome , saccharomyces cerevisiae , dna replication , gene , nucleoid , origin of replication , homologous recombination , escherichia coli
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.