Sequences of two kinetoplast DNA minicircles of Tryptanosoma brucei

Abstract

Kinetoplast DNA of Trypanosoma brucei is composed of a network of about 10,000 interlocked minicircle DNA molecules (1.0 kilobase) that are catenated with about 50 maxicircle DNA molecules (23 kilobases). Several different DNA . DNA hybridization techniques using individual minicircle DNA sequences cloned in Escherichia coli have indicated that each minicircle molecule contains about one-fourth of its sequence in common with most other minicircles and the remaining three-fourths in common with about 1 out of every 300 minicircles. We have determined the complete sequence of two cloned minicircle DNA molecules that were released from the total kinetoplast DNA network by different restriction enzymes; one minicircle is 1004 base pairs long, the other is 983 base pairs. Both are about 72% dA + dT. They share about 27% of their sequences; the largest continuous region in common is 122 base pairs of near-perfect homology. Twelve other regions of perfect homology equal to or greater than 10 base pairs are also present. Both sequences contain a large number of translation termination codons in all potential translation reading frames. The largest oligopeptide potentially specified by one minicircle sequence is 52 amino acids; the largest by the other minicircle sequence is 71 amino acids. One minicircle contains a decanucleotide sequence that is repeated in tandem five times. It is proposed that massive recombination among the interlocked minicircles in the kinetoplast DNA network may account for much of the homology observed in the two minicirce sequences.