HOMOLOGOUS RECOMBINATION BETWEEN DIRECT REPEAT SEQUENCES YIELDS P-GLYCOPROTEIN CONTAINING AMPLICONS IN ARSENITE RESISTANT LEISHMANIA

The protozoan parasite Leishmania often responds to drug pressure by a mplifying part of its genome. At least two loci derived from the same 800 kb chromosome were amplified either as extrachromosomal circles or linear fragments after sodium arsenite selection. A 50 kb linear ampl icon was detected in six independent arsenite mutants and revertants g rown in absence of arsenite rapidly lost the amplicon and part of thei r resistance. The circular extrachromosomal amplicons, all derived fro m the H locus of Leishmania, were characterized more extensively. In a ll cases, direct repeated sequences appeared to be involved in the for mation of circular amplicons. Most amplicons were generated after homo logous recombination between two linked P-glycoprotein genes. This rec ombination event was, in two cases, associated with the loss of one al lele of the chromosomal copy. A novel rearrangement point was found in a mutant where the amplicon was created by recombination between two 541 bp direct repeats surrounding the P-glycoprotein gene present at t he H locus. It is also at one of these repeats that an H circle with l arge inverted duplications was formed. We propose that the presence of repeated sequences in the H locus facilitates the amplification of th e drug resistance genes concentrated in this locus.