Structure of discontinuities in kinetoplast DNA-associated minicircles during S phase in Crithidia fasciculata.
Kinetoplast DNA (kDNA) is a novel form of mitochondrial DNA consisting of thousands of interlocked minicircles and 20-30 maxicircles. The minicircles replicate free of the kDNA network but nicks and gaps in the newly synthesized strands remain at the time of reattachment to the kDNA network. We show here that the steady-state population of replicated, network-associated minicircles only becomes repaired to the point of having nicks with a 3'OH and 5'deoxyribonucleoside monophosphate during S phase. These nicks represent the origin/terminus of the strand and occur within the replication origins (oriA and oriB) located 180 degrees apart on the minicircle. Minicircles containing a new L strand have a single nick within either oriA or oriB but not in both origins in the same molecule. The discontinuously synthesized H strand contains single nicks within both oriA and oriB in the same molecule implying that discontinuities between the H-strand Okazaki fragments become repaired except for the fragments initiated within the two origins. Nicks in L and H strands at the origins persist throughout S phase and only become ligated as a prelude to network division. The failure to ligate these nicks until just prior to network division is not due to inappropriate termini for ligation.
Molecular Biology Institute and Department of Microbiology, Immunology and Molecular Genetics, University of California Los Angeles, CA 90095-1570, USA.
Jane C
JC
Hines
Dan S
DS
Ray
D000818:Animals; D001483:Base Sequence; D016831:Crithidia fasciculata / Q000235:genetics*; D004260:DNA Repair; D004261:DNA Replication; D018105:DNA, Kinetoplast / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D008969:Molecular Sequence Data; D018741:Replication Origin; D016196:S Phase / Q000235:genetics*; D016415:Sequence Alignment
D018105:DNA, Kinetoplast; C034510:CTCGAG-specific type II deoxyribonucleases; D015252:Deoxyribonucleases, Type II Site-Specific