Hybridisation with a repetitive DNA probe reveals the presence of small chromosomes in Trypanosoma vivax.

We have isolated and cloned a tandemly repeating element from trypanosoma vivax for use as a species-specific DNA probe. The repeat hybridises only with DNA from T. vivax, not with DNA from other Salivarian trypanosome species (T. brucei spp., T. congolense, T. simiae). The monomer of the repeat is approximately 180 bp long and is 64% GC rich. Hybridisation of the cloned fragment with size-fractionated large DNA molecules of 3 T. vivax stocks revealed a band in the position expected for minichromosomes, although these were believed absent in T. vivax. This band migrated to the 100-250 kb area of the gel at 4 different pulse frequencies and also hybridised with a telomeric repeat probe from T. brucei. The band is unlikely to be simply degraded material, since it failed to hybridise with another highly repetitive sequence from T. vivax and was consistently present in different trypanosome preparations. We conclude that T. vivax does possess mini-chromosomes, although possibly only 1 or 2 per cell.