Genetic and functional analysis of mitochondrial DNA-encoded complex I genes.
Mammalian mitochondrial NADH dehydrogenase (complex I) is a multimeric complex consisting of at least 45 subunits, 7 of which are encoded by mitochondrial DNA (mtDNA). The function of these subunits is largely unknown. We have established an efficient method to isolate and characterize cells carrying mutations in various mtDNA-encoded complex I genes. With this method, 15 mouse cell lines with deficiencies in complex I-dependent respiration were obtained, and two near-homoplasmic mutations in mouse ND5 and ND6 genes were isolated. Furthermore, by generating a series of cell lines with the same nuclear background but different content of an mtDNA nonsense mutation, we analyzed the genetic and functional thresholds in mouse mitochondria. We found that in wild-type cells, about 40% of ND5 mRNA is in excess of that required to support a normal rate of ND5 subunit synthesis. However, there is no indication of compensatory upsurge in either transcription or translation with the increase in the proportion of mutant ND5 genes. Interestingly, the highest ND5 protein synthesis rate was just sufficient to support the maximum complex I-dependent respiration rate, suggesting a tight regulation at the translational level. In another line of research, we showed that the mitochondrial NADH-quinone oxidoreductase of Saccharomyces cerevisiae (NDI1), although consisting of a single subunit, can completely restore respiratory NADH dehydrogenase activity in mutant human cells that lack the essential mtDNA-encoded subunit ND4. In particular, in these transfected cells, the yeast enzyme becomes integrated into the human respiratory chain and fully restores the capacity of the cells to grow in galactose medium.
Bai
Yidong
Y
Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA. baiy@uthscsa.edu
Hu
Peiqing
P
Park
Jeong Soon
JS
Deng
Jian-Hong
JH
Song
Xiufeng
X
Chomyn
Anne
A
Yagi
Takao
T
Attardi
Giuseppe
G
D000818:Animals; D002460:Cell Line; D004272:DNA, Mitochondrial / Q000235:genetics*; D004579:Electron Transport / Q000502:physiology*; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics / Q000378:metabolism; D042967:Electron Transport Complex I / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D009154:Mutation; D014176:Protein Biosynthesis; D021122:Protein Subunits / Q000235:genetics* / Q000378:metabolism
D004272:DNA, Mitochondrial; D045222:Electron Transport Chain Complex Proteins; D021122:Protein Subunits; D042967:Electron Transport Complex I