Besides, its knockdown causes mRNA accumulation in the nucleus and decreasing of translation levels, confirming that this protein is a component of mRNA transcription/export pathway in trypanosomes. Moreover, we observed the presence of grouped gold particles at the edge of electron-dense chromatin regions. This distribution is similar to that of transcription sites, indicating that TcSub2 is located in active transcription regions. Analyses using indirect immunofluorescence combined with telomere FISH reinforced this notion because most of the protein does not colocalize with telomeres as indicated by the absence of TcSub2 signal over most of the telomeric repeats. To test this hypothesis, in situ labeling of nascent RNAs followed by the immunofluorescence of TcSub2 was analyzed 
by confocal microscopy. This approach allowed the detection of BrUTP-labeled nascent RNAs, which corresponded to active transcription sites, and TcSub2. Chloroquine Phosphate Post-transcriptional events are crucial for regulation of gene expression in trypanosomatids because of the absence of specific control mechanisms during transcription. Unlike most eukaryotic organisms, in which each gene transcribed by RNA Pol II has its own promoter, transcription in trypanosomatids is polycistronic without traditional promoter elements and genes in individual clusters do not necessarily code for functionally related proteins. Mature mRNAs are generated from primary transcripts by trans-splicing and polyadenylation and are then moved to the cytoplasm to be translated. In the context of posttranscriptional events, the machinery of mRNA export is poorly understood in trypanosomes and this pathway might be an important step in regulation of gene expression in these parasites. We were therefore interested in investigating the factors that could be involved in this pathway. The export of a few mRNAs in T. cruzi can be mediated by CRM1, a component of the RanGTP-exportin pathway. This pathway is commonly responsible for protein export but has no major role in mRNA export in higher eukaryotes. Most reports related to this topic come from model organisms, especially S. cerevisiae, and the bulk of mRNA is exported in a RanGTP independent pathway involving the THO/TREX complex. Based on our previous investigations, we started biological analysis of the most conserved component of the eukaryotic mRNA export pathway, the yeast DEAD-box RNA helicase Sub2. In the Folinic acid calcium salt pentahydrate present study we cloned the gene encoding the T. cruzi protein that is highly similar to Sub2/UAP56, and has been named TcSub2. Sub2/UAP56 is a component of the TREX multiprotein complex that links transcription with mRNA export. DEAD-box proteins are involved in the ATP-dependent unwinding of doublestranded RNA, displacement, RNA remodeling, or RNA/protein complexes. They are characterized by nine conserved motifs distributed in two domains. In general, motifs I and II are implicated in ATP binding and hydrolysis, with contributions from motif VI. Motif III is believed to couple ATP hydrolysis with RNA unwinding, whereas motifs IV, V, and VI contribute to RNA binding. We noted some changes of amino acid composition in the TcSub2 sequence when compared to the human sequence. However, these changes did not affect the molecular model of TcSub2 that is very similar to the UAP56 crystal structure. Although TcSub2 is highly conserved, it is unable to function as a substitute for SUB2. We speculate that this could be due to the specific functions of TcSub2 in T. cruzi because most transcripts in this parasite are processed by trans-splicing.