Molecular cloning and characterization of a gene encoding the 29-kDa proteasome subunit from Trypanosoma cruzi

Antiserum raised against purified Trypanosoma cruzi proteasomes was used to isolate two cDNA clones, tcpr29 and tcpr29B, and the corresponding genomic sequence, termed tcpr29A. Both cDNAs and the gene contain a 798-bp ORF, coding for a 266-amino acid protein, with a predicted molecular mass of 29 kDa. Sequence comparisons show that the protein encoded by tcpr29 belongs to the alpha6 subfamily of proteasome subunits. Southern analysis indicated that tcpr29 subunit is encoded by a single-copy gene which maps to chromosome 20 of the CL Brener clone. Allelic variants were found in other T. cruzi isolates, suggesting heterozygosity for the gene in some and homozygosity in other strains. A spliced-leader addition site was identified 123 bp upstream from the start codon, generating a stable 1.5-kb transcript. Western analysis revealed that tcpr29A is constitutively expressed during the life cycle of the parasite.

Molecular cloning and characterization of the DNA mismatch repair gene class 2 from the Trypanosoma cruzi

Genes with homology to the bacterial mutS gene, which encodes a protein involved in post-replication DNA mismatch repair, are known in several organisms. Using a degenerate PCR strategy, we cloned a Trypanosoma cruzi genomic DNA fragment homologous to the mutS gene class two (MSH2). This fragment was used as a probe to select the corresponding cDNAs from a T. cruzi cDNA library. The complete sequence of the gene (3304 bp), denominated TcMSH2, was obtained. The sequence contained an open reading frame of 2889 bp coding for a putative protein of 962 amino acids. Computational analyses of the amino acid sequence showed 36% identity with MSH2 proteins from other eukaryotes and revealed the presence of all functional domains of MutS proteins. Hybridization analyses indicated that the TcMSH2 gene is present as a single copy gene that is expressed in all forms of the T. cruzi life cycle. The role of the product of the TcMSH2 gene in mismatch repair was investigated by negative dominance phenotype analyses in Escherichia coli. When eukaryotic muts genes are expressed in a prokaryotic system, they increase the bacterial mutation rate. The same phenomenon was observed with the TcMSH2 cDNA, indicating that T. cruzi MSH2 interferes with the bacterial mismatch system. Phylogenetic analyses showed that the T. cruzi gene grouped with the MSH2 clade confirming the nature of the gene isolated in this work.