Recent developments from the Leishmania genome project

A first generation cosmid contig map of the Leishmania major Friedlin genom e has been constructed, and genomic sequencing is well underway. Chromosome 1 (Chr1) and Chr3 have been completely sequenced, and Chr4 is virtually co mplete. Sequencing of several other chromosomes is in progress and the comp lete genome sequence may be available as soon as 2003. More than 600 comple tely sequenced new genes have been identified, representing similar to 8% o f the total gene complement (similar to 8600 genes) of Leishmania. Notably, a large proportion (similar to 69%) of the genes remain unclassified, with 40% of these being potentially Leishmania- (or kinetoplastid-) specific. M ost interestingly, the genes are organized into large (>100-300 kb) polycis tronic clusters of adjacent genes on the same DNA strand. Chr1 contains two such clusters organized in a 'divergent' manner, whereas Chr3 contains two 'convergent' clusters, with a single 'divergent' gene at one telomere, wit h the two large clusters separated by a tRNA gene. Statistical analyses of Chr1 show that the 'divergent junction' region between the two polycistroni c gene clusters may be a candidate for an origin of DNA replication.