Alignment of T. brucei RBP42 and human G3BP1. (A) Multiple sequence alignments of two trypanosomatid RBP42s and two metazoa G3BP1s. Gene annotations are T. brucei (Tb927.6.4440), Leishmania major (LmjF.30.3090), Homo sapiens (G3BP1,Q13283, Gene identification 10146), and Mus musculus (P97855). The NTF-2 domain is overlined by a gray bar; the RNA recognition motif (RRM) domain is underlined by a white bar; and the three PxxP motifs in T. brucei are overlined with a black line. The single PxxP motif in the human and mouse genes is underlined. Numbering at the ends of lines identifies amino acid location for each organism. (B) Schematic comparison of T. brucei RBP42 and human G3BP1. RBP42 is 79% of the size of G3BP1 (drawing is approximately to scale). The NTF-2 domain (light gray), weakly acidic and acidic regions (dashed-stripe and striped), triple or single PxxP motifs (PxxP), RRM domain (white), and RRG-rich region (black) are shown. RBP42 and G3BP1 are similar but not identical; therefore, the trypanosome protein is named in accordance with the published trypanosomatid RNA-binding protein designation scheme (De Gaudenzi et al. 2005). Within the RRM, the RNP1 signature sequence motif (K/R) G (F/Y)(G/A)FVX(F/Y) is present in T. brucei RBP42 as KGYVFFDF (amino acids 311–319).