The accessory subunit of mitochondrial DNA polymerase gamma determines the DNA content of mitochondrial nucleoids in human cultured cells.
The accessory subunit of mitochondrial DNA polymerase gamma, POLGbeta, functions as a processivity factor in vitro. Here we show POLGbeta has additional roles in mitochondrial DNA metabolism. Mitochondrial DNA is arranged in nucleoprotein complexes, or nucleoids, which often contain multiple copies of the mitochondrial genome. Gene-silencing of POLGbeta increased nucleoid numbers, whereas over-expression of POLGbeta reduced the number and increased the size of mitochondrial nucleoids. Both increased and decreased expression of POLGbeta altered nucleoid structure and precipitated a marked decrease in 7S DNA molecules, which form short displacement-loops on mitochondrial DNA. Recombinant POLGbeta preferentially bound to plasmids with a short displacement-loop, in contrast to POLGalpha. These findings support the view that the mitochondrial D-loop acts as a protein recruitment centre, and suggest POLGbeta is a key factor in the organization of mitochondrial DNA in multigenomic nucleoprotein complexes.
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MRC-Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK.
Sembongi
H
H
He
J
J
Reyes
A
A
Yasukawa
T
T
Martinsson
P
P
Bailey
L J
LJ
Goffart
S
S
Boyd-Kirkup
J D
JD
Wong
T S
TS
Fersht
A R
AR
Spelbrink
J N
JN
Holt
I J
IJ
D045744:Cell Line, Tumor; D000074002:DNA Polymerase gamma; D004272:DNA, Mitochondrial / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008928:Mitochondria / Q000201:enzymology / Q000648:ultrastructure; D019384:Nucleic Acid Synthesis Inhibitors; D009698:Nucleoproteins / Q000378:metabolism; D010957:Plasmids / Q000737:chemistry; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference
D004272:DNA, Mitochondrial; D019384:Nucleic Acid Synthesis Inhibitors; D009698:Nucleoproteins; D021122:Protein Subunits; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; C544932:POLG2 protein, human