Abstract
Mitochondrial DNA is organized as a nucleoprotein complex called the nucleoid. Its major protein components have been identified in different organisms, but it is yet unknown whether nucleoids undergo any form of remodeling. Using an in organello ChIP-on-chip assay, we demonstrate that the DNA-bending protein Abf2 binds to most of the mitochondrial genome with a preference for GC-rich gene sequences. Thus, Abf2 is a bona fide mitochondrial DNA-packaging protein in vivo. Nucleoids form a more open structure under respiring growth conditions in which the ratio of Abf2 to mitochondrial DNA is decreased. Bifunctional nucleoid proteins Hsp60 and Ilv5 are recruited to nucleoids during glucose repression and amino-acid starvation, respectively. Thus, mitochondrial nucleoids in yeast are dynamic structures that are remodeled in response to metabolic cues. A mutant form of Hsp60 that causes mtDNA instability has altered submitochondrial localization, which suggests that nucleoid remodeling is essential for the maintenance of mitochondrial genome.