| Mitochondria play a central role in cellular energy provision. Their own genome codes for some of the subunits of the respiratory chain, but a majority are nuclear encoded. In addition, mitochondria must rely on imported nuclear gene products for transcription, replication, and repair.;Maintenance of the mitochondrial genome requires faithful replication. This is important during oogenesis because vast amounts of mitochondrial DNA (mtDNA) accumulate in oocytes and are packaged for organelle biogenesis. These mitochondria are stored and then partitioned to embryonic cells after fertilization. Mistakes made during replication, assembly or segregation of the mitochondrial nucleoid could be lethal or debilitating for the embryo.;A protein that may be responsible for the differential accumulation of mtDNA during Xenopus oogenesis and embryogenesis has been investigated. This nuclear encoded gene product, designated mtTFA, is an abundant HMG-box transcription factor. Like other HMG-box family members, mtTFA has architectural roles like bending, wrapping, unwinding, or packaging DNA. Mitochondrial transcription is linked to replication because aborted transcripts provide primers for replication. Therefore, when mtTFA binds to the control region, which contains promoters and the origin of heavy strand replication, the conditions are favorable for nucleic acid synthesis. Stimulation of transcription is concentration-dependent, and presumably, so is replication. The mtTFA-to-mtDNA ratios during development indicate that mtTFA levels are low when there is active DNA synthesis, and high when there is not. During late oogenesis, accumulated mtDNAs are packaged in a non-replicating state. It appears that at high concentrations of mtTFA, nucleic acid synthesis is not favorable and mtTFA takes on the role of organizing mtDNA. The data presented suggest that mtTFA not only participates in transcription, but also in the maintenance of mtDNA.;mtDNA is associated with proteins, and must be packaged into nucleoids after replication. mtTFA is the only well-characterized constituent of the nucleoid, as demonstrated biochemically by isolating protein-DNA complexes from Xenopus mitochondria. In this dissertation, two membrane proteins, COX and porin, have also been identified among proteins associated with the nucleoid. The methods described can be useful for identifying other components of the complexes which are necessary for maintenance of the mitochondrial genome. |
