Characterisation of three chromosomal ends of Leishmania major reveals transcriptional activity across arrays of reiterated and unique sequences

The 36 chromosomes of the parasite Leishmania major range in size from 200 kb to approximately 2.5 Mb and variation between homologues seems to be res tricted to the telomeric and subtelomeric regions. We have isolated three c osmids carrying the telomere hexameric repeat and assigned them to the extr eme location of chromosomes 3, 7 and 20. When considering the distribution of repetitive sequences, Southern analysis of the three chromosomal ends in dicated the existence of at least two classes of chromosomal extremities: o ne of them is composed almost exclusively of unique sequences and the other is characterised by patches of both reiterated and unique sequences. We de vised a transfection-based strategy that allowed the determination of a map of transcripts in each of the regions examined. Sequencing of the chromoso me 20 cosmid revealed the existence of a novel class of reiterated sequence , LST-R378, and 10 ORFs drawing a map of putative genes compatible with the map of transcripts. (C) 2001 Elsevier Science B.V. All rights reserved.