The Leishmania genome project: new insights into gene organization and function

The sequencing of Leishmania major Friedlin chromosome 1 (Chr1), Chr3, and Chr4 has been completed, and several other chromosomes are well underway. T he complete genome sequence should be available by 2003. Over 1,000 full-le ngth new genes have been identified, with the majority (similar to 75%) hav ing unknown function. Many of these may be Leishmania (or kinetoplastid) sp ecific. Most interestingly, the genes are organized into large (> 100-500 k b) polycistronic clusters of adjacent genes on the same DNA strand. Chr1 co ntains two such clusters organized in a "divergent" manner, i.e., the mRNAs for the two sets of genes are both transcribed towards the telomeres. Nucl ear run-on analysis suggests that transcription is initiated in both direct ions within the "divergent" region. Chr3 and Chr4 contain two "convergent" clusters, with a single "divergent" gene at one telomere of Chr3. Sequence analysis of several genes from the LD1 region of Chr35 indicates a high deg ree of sequence conservation between L. major and L. donovani/L. infantum w ithin protein-coding open reading frames (ORFs), with a lower degree of con servation within the non-coding regions. Immunization of mice with recombin ant antigen from two of these genes, BT1 (formerly ORFG) and ORFF, results in significant reduction in parasite burden following Leishmania challenge. Recombinant ORFF antigen shows promise as a serodiagnostic. We have also d eveloped a tetracycline-regulated promoter system, which allows us to modul ate gene expression in Leishmania.