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J. Cell Biol.,
Volume 143, Number 4, November 16, 1998 911-919
Department of Biological Chemistry, Johns Hopkins School of Medicine, Baltimore, Maryland 21205
Kinetoplast DNA (kDNA), the mitochondrial DNA in kinetoplastids, is a network containing
several thousand topologically interlocked minicircles.
We investigated cell cycle-dependent changes in the localization of kDNA replication enzymes by combining
immunofluorescence with either hydroxyurea synchronization or incorporation of fluorescein-dUTP into the
endogenous gaps of newly replicated minicircles. We
found that while both topoisomerase II and DNA polymerase 
colocalize in two antipodal sites flanking the
kDNA during replication, they behave differently at
other times. Polymerase is not detected by immunofluorescence either during cell division or G1, but is abruptly detected in the antipodal sites at the onset of
kDNA replication. In contrast, topoisomerase II is localized to sites at the network edge at all cell cycle
stages; usually it is found in two antipodal sites, but during cytokinesis each postscission daughter network is
associated with only a single site. During the subsequent G1, topoisomerase accumulates in a second localization site, forming the characteristic antipodal pattern. These data suggest that these sites at the network
periphery are permanent components of the mitochondrial architecture that function in kDNA replication.
;
topoisomerase II
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