This laboratory studies the mechanism of mitochondrial (mt) DNA
replication in the mammalian cell. MtDNA is a 16 kb, circular duplex DNA
which encodes 13 polypeptide subunits of the oxidative phosphorylation
pathway of the inner membrane of the mitochondrion. This mini chromosome
is maintained in all cells through repeated cycles of DNA synthesis to a
level of a few to several thousand copies. Our goal is to understand how
a new cycle of mtDNA synthesis is first initiated from the origin of
mtDNA replication and to eventually learn how the process of mtDNA
synthesis is controlled and regulated in response to the growth and
metabolic needs of the cell. In the past few years, we have begun to
realize how important the replication of mtDNA is to the health and long
term survival of the cell. Replication produces the multiple copies of
the genome which every cell needs in order to assemble a functional
respiratory chain for the synthesis of ATP. As well, replication
replaces the mtDNA circles that are continually being destroyed from the
high level of oxidative damage incurred from the respiratory chain.
Although mtDNA replication usually proceeds normally, under some
circumstances it produces errors, creating mutations in key genes. The
accumulation of such defects in mtDNA may be important and contribute to
aging, neurodegenerative disease and possibly even neoplasia.
For several years it has been known that replication of the mt genome
begins with the synthesis of one of the two strands of the DNA duplex,
the so-called heavy (H)-strand, from a specific site on the genome known
as the origin of H-strand replication (Ori H). Since the mtDNA
polymerase can not initiate new DNA chains de novo, synthesis of
this H-strand is dependent upon the production of an Ori H-specific
oligonucleotide primer. Although the creation of this primer represents
the first and one of the most important steps in mtDNA replication, the
enzymes and DNA binding proteins that orchestrate its synthesis have
until now remained elusive. Recently, my lab has finally succeeded in
developing a faithful in vitro assay system to study the
mechanism of H-strand priming.
Our ongoing results with this assay system suggest that the primer for
H-strand replication can be synthesized by a novel origin directed DNA
primase and not exclusively by the mtDNA RNA polymerase as widely
presumed. In addition, we are currently studying a newly
discovered mitochondrial DNA topoisomerase II activity, and other
mitochondrial enzyme activities that could help repair oxidative damage
incurred in mtDNA in vivo.
Selected Publications
Houmiel K, Gerschenson M, Low RL. (1993) Mitochondrial
endonuclease activity in the rat varies markedly among tissues in
relation to the rate of tissue metabolism. Biochem. Biophys. Acta
1079, 197-202. Gerschenson M, Low RL, Loehr J (1994) Levels of
the mitochondrial endonuclease during rat cardiac development implicate
a role for the enzyme in repair of oxidative damage. J. Mol. Cell.
Cardiol. 26, 31-40.
Fraser M, Low RL (1994) Fungal and mitochondrial nucleases. In Nucleases
(Robert R and Linn S, eds.), pp. 171-208. Cold Spring Harbor Press.
Gerschenson M, Houmiel KL, Low RL (1995) Endonuclease G from mammalian
nuclei is identical to the major endonuclease of mitochondria. Nucleic
Acids Res. 23, 88-97.
Tyler KL, Sokol RJ, Oerhaus SM, Le M, Karrer FM, Narkewicz MR, Tyson RW,
Murphy JR, Low R, Brown WR. (1998) Detection of reovirus RNA in
hepatobiliary tissues from patients with extrahepatic biliary atresia
and choledochal cysts. Hepatology, in press.
Nielsen-Preiss SM, Low RL (2000) Identification of a
beta-like DNA polymerase activity in bovine heart mitochondria.
Arch. Biochem. Biophys. 375, 229-240.
Low, R.L. and Gerschenson, M. (2002) Endonuclease G Isolation and Assays.
In Methods in Molecular Biology Series, vol. 197: Mitochondrial DNA:
Methods and Protocols. Ed. W.C. Copeland. Humana Press, Totowa, N.J.
Low, R.L. (2003) Mitochondria Endonuclease G function in apoptosis and
mtDNA metabolism: a historical review. Mitochondrion (in press).
CU Faculty PubMed Publications |
|
All PubMed Publications |
Back to Top
