Trypanosomes kinetoplast

Klingbeil MM, Drew ME, Liu Y et al. Unlocking the secrets of trypanosome kinetoplast DNA network replication. Ptotist 2001 132(4) 255-62. 

Ploubidou A Robinson DR, Docherty RC et al. Evidence for novel cell cycle checkpoints in trypanosomes Kinetoplast s egation and cytokinesis in the absence of mitosis. J Cell Sci 1999 112(Pt 24) 4641-50. 

Eukaryotic cells also have organelles, mitochondria (Fig. 24-6) and chloroplasts, that contain DNA. Mitochondrial DNA (mtDNA) molecules are much smaller than the nuclear chromosomes. In animal cells, mtDNA contains fewer than 20,000 bp (16,569 bp in human mtDNA) and is a circular duplex. Each mitochondrion typically has two to ten copies of this mtDNA molecule, and the number can rise to hundreds in certain cells when an embryo is undergoing cell differentiation. In a few organisms (trypanosomes, for example) each mitochondrion contains thousands of copies of mtDNA, organized into a complex and interlinked matrix known as a kinetoplast. Plant cell mtDNA ranges in size from... 

The kinetoplast DNA of trypanosomes (Fig. 5-16) consists of thousands of catenated circular DNA molecules. Among these the smaller minicircles always contain the sequence GGGGTTGGTGTAat their origins of replication. The minicircles are individually removed from the mass prior to replication. The two progeny circles are then both recatenated into the mass.462... 

Reevaluating the Kinetoplast as a Potential Target for Anti-Trypanosomal Dru ... 

Ray DS. Conserved sequence blocks in kinetoplast minidrcles fiom diverse spedes of trypanosomes. Mol CeU Biol 1989 9(3) 1365-7. 

Type I DNA topoisomerases were isolated from L donovam Trypanosoma cruz and Crithidia fasciculate The purified active enzymes (65 - 79 kDa) were ATP- independent and found to be sensitive to topoisomerase I specific inhibitor, camptothecin. Although immunolocalization studies for C fascicukta topoisomerase I showed that it is situated in the nucleus rather than the kinetoplast, it has been demonstrated in trypanosomes that camptothecin treatment induces WNA minicircle cleavage. This observation suggests a possible existence of topoisomerase I in the kinetoplast of trypanosomes. 

In some protozoa the mitochondria are few, in other numerous, and more often filled with tubules than with cristae. The solitary kinetoplast of trypanosomes, which contains DNA, arises by division of an earlier kinetoplast, and contains all the information needed to produce mitochondria (and a cytochrome system) when these parasites infect their second host, the insect in which they reproduce as crithidia (amastigotes) (Vickerman, 1962). 

The following anti-trypanosomal drugs bind irreversibly to, and disintegrate, the kinetoplast of Trypanosoma rhodesiense (in the mouse) without any effect on the cell s nucleus diminazine, ethidium, pentamidine, hydroxystilbamidine, and trypaflavine (Macadam and Williamson, 1972). The lack of a histone covering over the kinetoplast makes it more vulnerable than the nucleus to these drugs (Steinert, 1965). In place of mitochondria, some protozoa have hydrogeno-somes in which ferredoxin-activated enzymes, which convert pyruvate to acetyl-CoA, are selectively vulnerable to metronidazole. 

Kinetoplast a structure at the base of the single flagellum of a trypanosome. The K. has a high affinity for basic dyes, and was first observed early in the 20th century by light microscopy. Electron microscopy shows that the K. is a disc-like structure in the matrix of the cell s single mitochondrion. The K. has attracted biochemical interest because it contains an unusual form of highly catenated DNA, known as kinetoplast DNA (kDNA). See Catenane. 

In eukaryotic cells, the replication of cytoplasmic DNA is more susceptible to the action of intercalating dyes than the replication of chromosomal DNA. Well-known examples of this selective efficiency are (a) action of ethidium bromide on the kinetoplast of the trypanosomes, and (b) action of acriflavine on the mitochondrial DNA in yeasts (leading to petite ctAonie mutants). Such dyes are now used to study the importance of cytoplasmic DNA during morphogenesis. 

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