Gene expression in trypanosomes is controlled at the level of pre-mRNA maturation via trans-splicing and polyadenylation and through changes in mRNA stability. To identify the trans- acting factors involved in this regulation, we have used a degenerate PCR approach to clone genes encoding the RNA recognition motif (RRM) consensus. We have identified a single-copy gene encoding a protein (designated RRM1) which contains three consensus RRM motifs, two tandem copies of a retroviral gag-like CCHC 'zinc finger' and an arginine-serine (RS) rich region. Western blotting indicates that RRM1 is expressed in both procyclic and bloodstream-form trypanosomes and has an apparent mobility on SDS-PAGE of ca. 70 Kd. RRM1 is localized in the trypanosome nucleus in substructures which may be functionally analogous to the 'speckles' associated with cis-splicing in higher eukaryotic cells. The structure of RRM1, its pattern of expression and its intracellular location suggest that it may play a role in trans-splicing.