Nucleolar pre-ribosomal-associated protein 1 (Npa1) is required for ribosome biogenesis and operates in the same functional environment as Rsa3p and Dbp6p during early maturation of 60S ribosomal subunits []. The protein partners of Npa1p include eight putative helicases as well as the novel Npa2p factor. Npa1p can also associate with a subset of H/ACA and C/D small nucleolar RNPs (snoRNPs) involved in the chemical modification of residues in the vicinity of the peptidyl transferase centre []. The protein has also been referred to as Urb1.
