Trypanosoma vivax: linkage of the mini-exon (spliced leader) and 5S ribosomal RNA genes

Characterization of spliced leader genes of Trypanosoma ( Megatrypanum ) theileri : phylogeographical analysis of Brazilian isolates from cattle supports spatial clustering of genotypes and parity with ribosomal markers

Trypanosoma (Megatrypanum) theileri from cattle and trypanosomes of other artiodactyls form a clade of closely related species in analyses using ribosomal sequences. Analysis of polymorphic sequences of a larger number of trypanosomes from broader geographical origins is required to evaluate the clustering of isolates as suggested by previous studies. Here, we determined the sequences of the spliced leader (SL) genes of 21 isolates from cattle and 2 from water buffalo from distant regions of Brazil. Analysis of SL gene repeats revealed that the 5S rRNA gene is inserted within the intergenic region. Phylogeographical patterns inferred using SL sequences showed at least 5 major genotypes of T. theileri distributed in 2 strongly divergent lineages. Lineage TthI comprises genotypes IA and IB from buffalo and cattle, respectively, from the Southeast and Central regions, whereas genotype IC is restricted to cattle from the Southern region. Lineage TthII includes cattle genotypes IIA, which is restricted to the North and Northeast, and IIB, found in the Centre, West, North and Northeast. PCR-RFLP of SL genes revealed valuable markers for genotyping T. theileri. The results of this study emphasize the genetic complexity and corroborate the geographical structuring of T. theileri genotypes found in cattle.

Comparative analyses among the Trichomonas vaginalis, Trichomonas tenax, and Tritrichomonas foetus 5S ribosomal RNA genes

The 5S ribosomal RNA (5S rRNA) is an essential component of ribosomes. Throughout evolution, variation is found among 5S rRNA genes regarding their chromosomal localization, copy number, and intergenic regions. In this report, we describe and compare the gene sequences, motifs, genomic copy number, and chromosomal localization of the Trichomonas vaginalis, Trichomonas tenax, and Tritrichomonas foetus 5S rRNA genes. T. vaginalis and T. foetus have a single type of 5S rRNA-coding region, whereas two types were found in T. tenax. The sequence identities among the three organisms are between 94 and 97%. The intergenic regions are more divergent in sequence and size with characteristic species-specific motifs. The T. foetus 5S rRNA gene has larger and more complex intergenic regions, which contain either an ubiquitin gene or repeated sequences. The 5S rRNA genes were located in Trichomonads chromosomes by fluorescent in situ hybridization.

The transcription promoter of the spliced leader gene from Trypanosoma cruzi

A putative promoter element responsible for transcription of the spliced leader (SL) gene of Trypanosoma cruzi was identified by overlapping deletion and linker scanning analyses of the upstream flanking sequences using the bacterial chloramphenicol acetyltransferase (CAT) gene as a reporter in transient transfections of cultured epimastigotes. Deletion or substitution of a proximal sequence element (PSE) between positions -53 and -40 relative to the transcription start point eliminated CAT gene expression. Comparison of SL genes from several strains of T. cruzi revealed two alternative sequence patterns for the putative SL PSE, both composed of a short run of purines followed by a run of pyrimidines. Moreover, an examination of these sequences supports the subdivision of T. cruzi isolates into two divergent groups. Double-stranded oligonucleotides containing the sequence of the PSE exhibited specific gel mobility shifts after incubation with T. cruzi nuclear extracts, suggesting that a transcription factor binds this site. Finally, experiments designed to increase the level of CAT expression from the SL promoter suggest that it is not a strong promoter in cultured T. cruzi epimastigotes.

Organization of mini-exon and 5S rRNA genes in the kinetoplastid Trypanoplasma borreli

Mini-exon gene repeats from Trypanoplasma borreli, which belongs to the Cryptobiidae family of the Bodonina suborder of the Kinetoplastida, were isolated by PCR amplification and cloning. The presence of kinetoplastid-like mini-exon genes in T. borreli is consistent with the taxonomic status of this organism as a kinetoplastid protozoan. Two families of repeats were found: 597 nt (T1) and 794 nt (T2), each of which encodes an approximately 95-nt medRNA transcript. The T1 repeats also contain a complete 5S rRNA gene on the complementary strand. The T2 repeats contain a defective copy of a 5S gene, in which the 5' portion is absent. The intergenic regions between the 5'-ends of the mini-exon genes and the 5S rRNA genes in the T1 and T2 repeats are highly diverged. All or most mini-exon genes and 5S genes are located within either the T1 or the T2 repeats. The T1 repeats were localized to a megabase-size chromosome, while the T2 repeats were localized within at least 4 large chromosomes.