Fig. 6. npo encodes a conserved, eukaryotic RNA-binding protein. (A) CLUSTALW alignment of Npo-related proteins from divergent eukaryotes reveals a high degree of conservation, particularly within RRM regions. Dark shading indicates amino acid identity and light shading indicates similarity. Red line indicates canonical RNA recognition motifs. (B) Conservation of RRM-domain configuration between Npo-related proteins. We show a manual alignment of RRM domains identified by RPS blast search of the GenBank conserved domain database (CDD). Domain numbering system was guided by CLUSTALW alignments as shown in panel A. Asterisk indicates site of termination codon encoded by npo^fW07-g. GenBank Accession Numbers are as follows: Human, NP_055667; Drosophila, AAM29657; C. elegans, NP502432; S. cerevisiae, NP_015437; Arabidopsis, CAB40378. (C) Npo binding of homopolymeric RNA. [³⁵S]-labeled Npo protein produced by in vitro transcription/translation was incubated with solid support-bound homopolymeric RNA of the indicated base composition. After several washes, the radioactivity from bound and input protein was quantitated by autoradiography and digital densitometry. The percent bound was highest for poly G and poly U. Npo⁹²⁶ indicates full-length wild-type protein, Npo²²⁰ indicates the truncated mutant. Error bars indicate±s.e.m. from three independent measurements.