Homologous recombination between direct repeat sequences yields P-glycoprotein containing amplicons in arsenite...

The protozoan parasite Leishmania often responds to drug pressure by amplifying 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 amplicon was detected in six independent arsenite mutants and revertants grown in absence of arsenite rapidly lost the amplicon and part of their resistance. The circular extrachromosomal amplicons, all derived from the H locus of Leishmania, were characterized more extensively. In all cases, direct repeated sequences appeared to be involved in the formation of circular amplicons. Most amplicons were generated after homologous recombination between two linked P-glycoprotein genes. This recombination event was, in two cases, associated with the loss of one allele 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 the H locus. It is also at one of these repeats that an H circle with large inverted duplications was formed. We propose that the presence of repeated sequences in the H locus facilitates the amplification of the drug resistance genes concentrated in this locus.