Free minicircles of kinetoplast DNA in Crithidia fasciculata

Leishmaniasis and malaria: new tools for epidemiologic analysis

Parasitic diseases are still prevalent in many parts of the world, causing both human suffering and economic loss. Recent developments in biotechnology, such as the use of monoclonal antibodies and recombinant DNA, have the potential for providing both more extensive and detailed information on the parasite in the infected human and in insect vectors. New methods of detection, both in man and insect vectors, have been developed for two parasitic diseases, leishmaniasis and malaria. These new methodologies will be important in epidemiologic studies on the prevalence and transmission of these parasitic diseases.

A simple procedure for the preparation of pure kinetoplast DNA network free of nuclear DNA from the kinetoplast hemoflagellate Leishmania donovani

A simple, inexpensive procedure for preparing pure kinetoplast DNA network from Leishmania donovani is described. L. donovani promastigotes were lysed by incubating with pronase in presence of sodium dodecylsulfate. Crude kinetoplast DNA networks were obtained by centrifugation of the lysate through a 20% sucrose solution. The pellet containing kinetoplast DNA was deproteinized by phenol extraction. Contaminating nuclear DNAs were removed by denaturation with alkali, neutralization, and addition of polyethylene glycol-8000 to a concentration of 10% to facilitate precipitation of kinetoplast DNA. kDNA isolated after centrifugation was deproteinized several times with phenol and finally precipitated with ethanol. The average yield by this procedure is 30-50 micrograms of kDNA per gram of wet cells. By slot-blot hybridization with a nuclear DNA probe, no nuclear DNA contamination of the kDNA networks could be detected.

Levels of topoisomerase II and DNA polymerase alpha are regulated independently in developing neuronal nuclei

A possible correlation between activity levels of topoisomerase II and DNA polymerase alpha was studied in neuronal nuclei from developing rat brain. A high level of canonical topoisomerase II activity was detected in neuronal nuclei throughout the development even at a late stage (28 days after birth) when the activity of DNA polymerase alpha decreased to less than 2% of the fetal level. Thus, in contrast to other systems, topoisomerase II does not change in parallel with DNA polymerase alpha during neuronal development. Our results suggest that topoisomerase II is required to maintain some fundamental processes in differentiated cells, including transcription.

The potential of using recombinant DNA species-specific probes for the identification of tropical Leishmania

Human leishmaniasis is a world-wide public health problem with more than 400000 new reported cases/year (Anon, 1984) in the tropics and subtropics. Were (1985) has estimated that Leishmaniases affect about 20 million people in the Third World. In hospitals where treatment is available, initially all positive cases are treated equally; it is the prognosis and follow-up that varies according to the causative organism. A wide variety of species or subspecies ofLeishmaniamay be present in a small verrucose lesion developing after an infected sandfly bite or appear in lesions as the disease progresses. Depending on whichLeishmaniais present a clinial decision must be made whether to treat with drugs of varying toxicity or not.

A 189-bp fragment of Crithidia fasciculata maxicircle DNA confers autonomous replication in Saccharomyces cerevisiae

A 189-bp fragment capable of promoting high-frequency transformation in Saccharomyces cerevisiae has been isolated from the maxicircle of the insect trypanosomatid Crithidia fasciculata. Chimeric plasmids containing this autonomously replicating sequence (ars) are maintained as extrachromosomal elements in S. cerevisiae. The nucleotide sequence of the maxicircle fragment, termed ars189, has been determined, and its position has been mapped in the maxicircle. The ars189 fragment has an A + T content of 79.4% and shows a large asymmetry in the distribution of adenine and thymine residues between the two strands. In one strand (the T strand) thymine accounts for 118 out of 189 nucleotides while adenine accounts for only 32 nucleotides. The ars189 DNA does not hybridize with minicircles, and its sequence appears to be unique in the C. fasciculata maxicircle genome. This sequence also shows extensive homology to a sequence within a 2.6-kb ars fragment of the Leishmania tarentolae maxicircle. In addition, ars189 contains two copies of a yeast consensus ars sequence (A/T)TTTATPuTTT(T/A).

Homogeneous and heterogeneous mini-circle subpopulations in Trypanosoma cruzi kinetoplast DNA

The small circular components (mini-circles) from Trypanosoma cruzi kinetoplast DNA (kDNA) were cloned in the plasmid vector pBR325. These clones have been used before to demonstrate the rapid evolution of mini-circle subpopulations (S anchez , D.O., Frasch , A.C.C., Carrasco , A.E., Gonzalez Cappa , S.M., Isola , E. and Stoppani , A.O.M. (1984) Mol. Biochem. Parasitol ., in the press). We have now analyzed the cloned molecules and used them to study some structural characteristics of T. cruzi mini-circles and their distribution in total kDNA restriction endonuclease digests. Most molecules partially conserved TaqI, HaeIII and HapII site clusters (constant regions) separated by one-quarter of the total mini-circle length, also detected in total kDNA digests. In addition, in one of the cloned mini-circles, the constant region was present only once, instead of four times as expected. Outside the conserved regions, the mini-circles diverged enough so that no cross-hybridization took place even under relaxed conditions. The recombinant molecules were used to probe total kDNA digests from T. cruzi. Some of them hybridized with most restriction endonuclease kDNA fragments, while one cloned mini-circle ( pTck -14) detected only its homologous subpopulation. The mini-circles detected with the latter probe proved to be nearly homogeneous, and were present in the proportion of 1/20 molecules. These results suggest that some of the generated molecules might have acquired a higher replication rate, giving rise to the homogeneous subpopulation detected. Further mutations, insertions and/or deletions, together with recombination between molecules, would bring this process to an end.

Sequence heterogeneity and anomalous electrophoretic mobility of kinetoplast minicircle DNA from Leishmania tarentolae

Several unit-length minicircles from the kinetoplast DNA of Leishmania tarentolae were cloned into pBR322 and into M13 phage vectors. The complete nucleotide sequences of three different partially homologous minicircles were obtained. The molecules contained a region of approx. 80% sequence homology extending for 160-270 bp and a region unique to each minicircle . A 14-mer was found to be conserved in all kinetoplast minicircle sequences reported to date. The frequency distributions of various minicircle sequence classes in L. tarentolae were obtained by quantitative gel electrophoresis and by examination of the "T ladder" patterns of minicircles randomly cloned into M13 at several sites. By these methods we could assign approx. 50% of the total minicircle DNA into a minimum of five sequence classes. A sequence-dependent polyacrylamide gel migration abnormality was observed with several minicircle fragments both cloned and uncloned. The abnormality was dependent on the presence of a portion of the conserved region of the minicircle .

Replication of kinetoplast DNA maxicircles

The kinetoplast DNA of Crithidia fasciculata is a massive network composed of thousands of topologically interlocked circles. Most of these circles are minicircles (2.5 kb), and about 50 are maxicircles (37 kb). Previous studies showed that minicircles replicate, after release from the network, via Cairns (theta) intermediates. Here we show that maxicircles replicate, while attached to the network, by an entirely different mechanism involving rolling circle intermediates. After the network-bound maxicircle has finished replication, the branch of the rolling circle is apparently cleaved off to form a linear free maxicircle. A restriction map of the linearized free maxicircles shows that these molecules have unique termini, one of which presumably corresponds to the replication origin.

A unique ATP-dependent DNA topoisomerase from trypanosomatids

Crithidia fasciculata DNA topoisomerase (22) has been purified to near homogeneity from trypanosomatid cell extracts. The purified enzyme catalyzes the reversible interconversion of monomeric duplex DNA circles and catenanes in an ATP dependent reaction. Reversible catenane formation is affected by the ionic strength and is dependent upon the action of a crithidial DNA binding protein, which could be substituted for the polyamine spermidine. Covalently sealed DNA circles are specifically used as substrates for decatenation. Nicking, but not relaxation per se, inhibits network decatenation and has little or no effect on catenane formation. The catalytic properties of this enzyme and its potential role in the prereplication release and post replication reattachment of kDNA minicircles are discussed.

The kinetoplast of DNA of Trypanosoma gambiense: comparison with the kDNA of Trypanosoma equiperdum

The molecular components of the kinetoplast DNA (kDNA) network of Trypanosoma gambiense have been studied and compared with those of the very closely related species T. equiperdum, previously studied in detail. The kDNA of T. gambiense contains about 80 maxicircles of 20 kilobase pairs and 4000 minicircles of 1 kilobase pairs. The restriction cleavage sites of 7 restriction endonucleases have been mapped on the T. gambiense maxicircle. The majority of these sites were also found in T. equiperdum maxicircles; however their relative positions which are different do not allow us to conclude to relatedness of maps. Maxicircles of the Cairn or of the rolling circle type have been observed and thought to be replicative intermediates. Experiments on renaturation kinetics and hybridization after blotting transfer, show that T. gambiense and T. equiperdum maxicircles have base sequences in common. The T. gambiense minicircles are heterogeneous in base sequence, in contrast to the T. equiperdum minicircles which are homogeneous. The minicircles of the two species have also common base sequences.

Workshop no. 6. Structure, function and evolution of kinetoplast DNA

The kinetoplast DNA (kDNA) of kinetoplastidae was the first mitochondrial DNA (mtDNA) to be discovered, and with its unusual network structure, consisting of more than 104catenated DNA circles, it is without equal in nature. Analysis of networks from various genera (reviewed by Borst & Hoeijmakers (1979a) and Englund (1980)) has shown that they always consist of two components: mini-circles and maxi-circles (see Table 1). The mini-circles are the major component and deterraine the size and sliape of networks. They vary in size between 1 and 3 kilo-base pairs (kb = 1000 base pairs (bp)), they are heterogeneous in sequence, their sequence evolves rapidly and their function is not yet known. The maxi-circles, on the other hand, are homogeneous in sequence, their sequence is conserved and they probably represent the counterpart of mtDNA in other organisms.