Two families of RNA binding proteins from Trypanosoma brucei associate in a direct protein-protein interaction

We have previously reported the identification of two closely related RNA binding proteins from Trypanosoma brucei, termed p34 and p37. The predicted primary structures of the two proteins are highly homologous with one major difference, an 18 amino acid insertion in the N-terminal region of p37. These two proteins are localized to the nucleus based on immunofluorescence microscopy. Recently, we have shown that p34 and p37 interact with T. brucei 5S rRNA. In order to gain further insight into their function, we have utilized protein affinity chromatography and immune capture approaches to identify T. brucei proteins which associate with p34 and p37. We demonstrate here an interaction of both p34 and p37 with the NOPP44/46 proteins, identified in T. brucei as a family of tyrosine-phosphorylated RNA binding proteins primarily localized to the nucleolus. This interaction was mapped to the RNA-binding region of p34/p37 and an acidic region of NOPP44/46 by protein affinity chromatography using recombinant deletion constructs of p34 and p37 and yeast two-hybrid analysis. These data may suggest a role for p34 and p37 and NOPP44/46 in the import and/or assembly pathway of T. brucei 5S rRNA in ribosome biogenesis.