EXPRESSION OF THE LEISHMANIA-TARENTOLAE UBIQUITIN-ENCODING AND MINI-EXON GENES

To develop models for transcription and trans-splicing in kinetoplasti d protozoa, we have characterized ubiquitin (Ubi) gene organization an d mRNA processing in Leishmania tarentolae (Lt). Three ubi loci were c haracterized: two discrete Ubi-extension protein 52 (EP52)-encoding ge nes (ubiA and ubiB) and a polymorphic polyubiquitin-encoding gene (ubi C). The three loci resided on chromosomes of 2.05 Mb, 630 kb and 2.9 M b, respectively. On the basis of upstream flanking gene identity, ubiB appears to be the homologue of the tandemly repeated ubi-EP52/1 and 2 in Trypanosoma brucei (Tb). Similar to Trypanosoma cruzi, Lt did not contain a homologue of the ubi-EP76 that has been found in Saccharomyc es cerevisiae and multicellular organisms. All three Lt ubi loci were transcribed. The primary transcripts from the ubi loci were processed at the 5'-end by trans-splicing with the mini-exon. A Lt mini-exon gen e (min) that gave rise to a 95-nt primary transcript, which is the sec ond template in the trans-splicing reaction, was also characterized.