Linear amplification of PTR1 as a large inverted duplication. (a) Genomic organization of the PTR1 locus in L. infantum and relative gene expression data as determined by DNA microarrays in L. infantum MTX20.5. Note that all genes from the telomere up to LinJ23_V3.0380 showed increased levels of expression in the MTX20.5 mutant compared to wild-type cells. (b) Chromosome size PFGE of Leishmania cells. Ethidium bromide (Et-Br) stained gel, or blotted gels hybridized to a PTR1 probe or to a probe containing the telomeric repeats are shown. Sizes were determined using a yeast molecular weight marker (Biorad). (c) Model for the formation of the extrachromosomal PTR1 linear amplicon generated through annealing of homologous inverted repeats (Figure S2 in Additional data file 2). This annealing could be facilitated by a block in replication. (d) PCR with primer pairs 23a and 23b or 23c and 23d to support the model shown in (c). Lane 1, L. infantum wild-type cells; lane 2, L. infantum MTX20.5.