Kinetoplast maxicircle DNA replication in Crithidia fasciculata and Trypanosoma brucei.
Kinetoplast DNA, the mitochondrial DNA of trypanosomatids, is composed of several thousand minicircles and a few dozen maxicircles, all of which are topologically interlocked in a giant network. We have studied the replication of maxicircle DNA, using electron microscopy to analyze replication intermediates from both Crithidia fasciculata and Trypanosoma brucei. Replication intermediates were stabilized against branch migration by introducing DNA interstrand cross-links in vivo with 4,5',8-trimethylpsoralen and UV radiation. Electron microscopy of individual maxicircles resulting from a topoisomerase II decatenation of kinetoplast DNA networks revealed intact maxicircle theta structures. Analysis of maxicircle DNA linearized by restriction enzyme cleavage revealed branched replication intermediates derived from theta structures. Measurements of the linearized branched molecules in both parasites indicate that replication initiates in the variable region (a noncoding segment characterized by repetitive sequences) and proceeds unidirectionally, clockwise on the standard map.
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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Carpenter
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Englund
D000818:Animals; D001483:Base Sequence; D016831:Crithidia fasciculata / Q000235:genetics* / Q000378:metabolism; D003432:Cross-Linking Reagents; D004261:DNA Replication; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D018105:DNA, Kinetoplast / Q000096:biosynthesis* / Q000302:isolation & purification / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D015183:Restriction Mapping; D013045:Species Specificity; D014307:Trioxsalen / Q000494:pharmacology; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism
D003432:Cross-Linking Reagents; D018105:DNA, Kinetoplast; D004250:DNA Topoisomerases, Type II; D014307:Trioxsalen