title: Maintenance of mitochondrial genome distribution by mitochondrial AAA+ protein ClpX.
abstract: The segregation of mitochondrial DNA (mtDNA) is important for the maintenance and transmission of the genome between generations. Recently, we clarified that human mitochondrial transcription factor A (TFAM) is required for equal distribution and symmetric segregation of mtDNA in cultured cells; however, the molecular mechanism involved is largely unknown. ClpX is an ATPase associated with various cellular activities (AAA+) proteins that localize to the mitochondrial matrix and is suggested to associate with mtDNA. In this study, we found that RNAi-mediated knockdown of ClpX in HeLa cells resulted in enlarged mtDNA nucleoids, which is very similar to that observed in TFAM-knockdown cells in several properties. The expression of TFAM protein was not significantly reduced in ClpX-knockdown cells. However, the enlarged mtDNA nucleoids caused by ClpX-knockdown were suppressed by overexpression of recombinant TFAM and the phenotype was not observed in knockdown with ClpP, a protease subunit of ClpXP. Endogenous ClpX and TFAM exist in close vicinity, and ClpX enhanced DNA-binding activity of TFAM in vitro. These results suggest that human ClpX, a novel mtDNA regulator, maintains mtDNA nucleoid distribution through TFAM function as a chaperone rather than as a protease and its involvement in mtDNA segregation.
authors: Jichi Medical University, Department of Biochemistry, Tochigi 329-0498, Japan. kasa@jichi.ac.jp
authors: Katsumi
authors: K
authors: Kasashima
authors: Megumi
authors: M
authors: Sumitani
authors: Hitoshi
authors: H
authors: Endo
mesh_terms: D001665:Binding Sites; D004272:DNA, Mitochondrial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D049071:Endopeptidase Clp / Q000235:genetics / Q000378:metabolism*; D054629:Genome, Mitochondrial; D006367:HeLa Cells; D006801:Humans; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D024101:Mitochondrial Proteins; C499631:TFAM protein, human; D014157:Transcription Factors; D049071:Endopeptidase Clp; C528384:CLPX protein, human