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A clone bank from Trypanosoma cruzi DNA was constructed in the plasmid vector pBR325 and screened with total labelled DNA from the same parasite. The experimental conditions used enable recombinant clones containing repetitive sequences to be detected. 2% of the clones gave a strong positive signal. Half of them carried mini-circle sequences but the other half contained repetitive sequences from the nuclear genome. 50% of all colonies showed up more weakly suggesting that half of the trypanosome DNA fragments carried few repetitive elements. One family of repeats, present in two clones from different genomic regions, hybridized with a broad range of nuclear DNA fragment sizes. Moreover, one of these clones had at least two kinds of elements with no common sequences. A third clone, detected under the same conditions, hybridized with distinct nuclear DNA bands. The number of copies estimated for the latter was much lower than the number of homologous sequences detected in nuclear DNA with the former two. This third recombinant plasmid proved useful to differentiate among closely related trypanosome stocks. Neither poly(A)+ or poly(A)- RNA, nor the 50 kilobase pair band corresponding to the satellite DNA already described in trypanosomes, contribute to the repeats present within these recombinant DNAs. Sequences with some degree of homology were found in the nuclear genome of T. brucei and Crithidia fasciculata.

The presence of isolate-specific Trypanosoma cruzi minicircles has been shown in the kinetoplast DNA of this parasite. This led to the rapid identification of isolates and clones of trypanosomes by means of 'dot-spot' hybridizations with molecularly cloned minicircle probes. Unexpectedly, whole kDNAs were also suitable as probes for this purpose, provided that filters were washed under stringent conditions. This was attributed to the presence of the above-mentioned isolate-specific minicircle sequences. The fact that parasites could be directly spotted onto nitrocellulose filters simplified the rapid routine screening of a large number of samples.