Résumé
A mitotically stable linear extra chromosome obtained in a Leishmania donovani strain rendered mycophenolic
acid-resistant has been physically mapped. This 290-kb chromosome
has an inverted duplicated structure around a central inversion region,
and is derived from a conservative amplification event of a ∼140-kb subtelomeric
end of chromosome 19. Large-sized targeted deletions of the central
region were performed through homologous recombination using three
specific transfection vectors. The size of the extra chromosome
was thus successfully reduced from 290 to 260, 200 and 120 kb respectively.
The mitotic stability of these chromosomes was then analysed in
drug-free cultures over >140 days. Results differed according
to the deletion created. By contrast with the smallest deletion
the two largest deletions altered mitotic stability, leading to
progressive loss of the size-reduced chromosomes with similar kinetics
in both mutants. The 30-kb region common to both deletions
may therefore be considered as involved in mitotic stability. A 44-kb
contig covering this region could be assembled and sequenced. The
analysis of this sequence did not reveal any sequence elements typical
of centromeric DNA. By contrast, its enrichment in homopolymer tracts
suggests that this region might contain an origin of replication.