The packaging of mitochondrial DNA (mtDNA) into DNA-protein assemblies called 
nucleoids provides an efficient segregating unit of mtDNA, coordinating mtDNA's 
involvement in cellular metabolism. From the early discovery of mtDNA as 
"extranuclear" genetic material, its organization into nucleoids and integration 
into both the mitochondrial organellar network and the cell at large via a 
variety of signal transduction pathways, mtDNA is a crucial component of the 
cell's homeostatic network. The mitochondrial nucleoid is composed of a set of 
DNA-binding core proteins involved in mtDNA maintenance and transcription, and a 
range of peripheral factors, which are components of signaling pathways 
controlling mitochondrial biogenesis, metabolism, apoptosis, and retrograde 
mitochondria-to-nucleus signaling. The molecular interactions of nucleoid 
components with the organellar network and cellular signaling pathways provide 
exciting clues to the dynamic integration of mtDNA into cellular metabolic 
homeostasis.