A novel type of single-stranded nucleic acid binding protein recognizing a highly frequent motif in the intergenic regions of Trypanosoma cruzi

Abstract

Regulation of gene expression in trypanosomatids is not yet well understood. Genes are organized in long polycistronic transcriptional units separated by intergenic regions that may contain the signaling information for nucleic acid processing. Poly-dinucleotides are frequent in these regions and have been proposed to be involved in regulation of gene expression. Previously, we have reported that [dT–dG] are highly frequent, asymmetrically strand distributed, and constitute targets for specific protein binding [Biochem. Biophys. Res. Commun. 287 (2001) 98]. Here, we present the purification and characterization of a new type of single stranded nucleic acid binding protein (Tc38) that recognizes specifically the motif poly[dT–dG] in this parasite. The protein has a deduced molecular weight of 38 kDa and its salient characteristics include an isoelectric point of 9.34, a high frequency of Ser, Leu, and di-amino acids. Neither compositional nor architectural conserved domains could be detected in database searches. Recombinant Tc38 was expressed as a GST fusion protein, purified, and used to analyze target specificity by electrophoretic mobility shift assays. The unusual characteristics of the protein together with the peculiar features of the specific nucleic acid target suggest the existence of a novel event that may be involved in the mechanisms of gene expression in trypanosomatids.