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Journal of Biochemistry Advance Access originally published online on July 30, 2009
Journal of Biochemistry 2009 146(5):725-732; doi:10.1093/jb/mvp118
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© The Authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved

Association of a Novel Mitochondrial Protein M19 with Mitochondrial Nucleoids

Megumi Sumitani1,*, Katsumi Kasashima1,*, Eriko Ohta1, Dongchon Kang2 and Hitoshi Endo1,{dagger}

1Department of Biochemistry, Jichi Medical University, Tochigi 329-0498; and 2Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan

{dagger}To whom correspondence should be addressed. Tel: +81-285-58-7322, Fax: +81-285-44-1827, E-mail: hendo{at}jichi.ac.jp

Received May 13, 2009; Accepted July 20, 2009


  Abstract

We have identified a novel mitochondrial protein, termed M19, by proteomic analysis of mitochondrial membrane proteins from HeLa cells. M19 is highly conserved among vertebrates, and possesses no homologous domains with other known proteins. By northern and western blotting, mouse M19 was shown to be expressed in various tissues, and to be especially abundant in the brain. Human M19 (hM19) is present in mitochondria, and protease-protection experiment showed it to be sublocalized in the matrix space. Carboxy-terminally tagged hM19 appeared as spotted signals within mitochondria and co-localized with signals arising from mitochondrial DNA (mtDNA), suggesting the inclusion of M19 in the mtDNA–protein complex (mitochondrial nucleoids). Fractionation of mitochondrial nucleoids from HeLa cells revealed that hM19 has a similar distribution pattern like that of known nucleoid components, such as mtSSB and PHBs, and surely exists in the nucleoid fraction. Furthermore, expression of M19 is closely related to the amount of mtDNA, because it was down-regulated in mtDNA-depleted {rho}0 HeLa cells. These results indicate that M19 associates with the nucleoid and likely regulates the organization and metabolism of mtDNA.

Key Words: mitochondria, mitochondrial protein, mitochondrial nucleoids, mtDNA

Abbreviations: CPS1, carbamoyl-phosphate synthetase 1; cyt.c, cytochrome c; FISH, Fluorescent in situ hybridization; LONP1, lon peptidase 1; mtDNA, mitochondrial DNA; mtSSB, mitochondrial single-stranded DNA-binding protein; OPA1, optic atrophy 1; PDHE2, pyruvate dehydrogenase E2; PDIP38, polymerase delta interacting protein 38; PHB, prohibitin; PHBs, prohibitin proteins; PMF, post-mitochondrial faction; TFAM, mitochondrial trnscription factor A; WCE, whole cell extract

*These authors equally contributed to this work.


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