PWP1 functions in ribosomal large-subunit biogenesis. (a) The expression pattern of mouse Pwp1 is similar to that of most known RNA-processing proteins. (b) The domain structures of Pwp1 homologs identified by BLASTP searches. Accession number and amino-acid length is given. We identified a single strong match in each of the species shown. Domains were identified by CDD search . (c) A northern blot showing the accumulation of 35S rRNA precursor (blue arrow), reduction in other rRNA precursors (top panel), and reduction in 25S rRNA (red arrow) in the yeast TetO7-PWP1 mutant (strain TH_2220) in comparison to the parental wild-type strain (R1158) . The U2 spliceosomal RNA is shown for comparison; its apparent abundance is increased because 5 μg RNA was loaded per lane, and the relative proportion of rRNA to snRNA is decreased in the mutant. Blotting procedures and probes were as previously described . (d) Affinity-purification of yeast Pwp1p-TAP reveals association with proteins known to function in ribosomal large-subunit biogenesis (Ebp2p, Nop12p, Brx1p) as well as a subset of ribosomal proteins. The asterisks mark degradation products of Pwp1p-TAP.