Npa1p is required for ribosome biogenesis and operates in the same functional environment as Rsa3p and Dbp6p during early maturation of 60S ribosomal subunits [1]. 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 [2]. The protein has also been referred to as Urb1, and this domain at the N-terminal is one of several conserved regions along the length.

1: Npa1p is an essential trans-acting factor required for an early step in the assembly of 60S ribosomal subunits in Saccharomyces cerevisiae. Rosado IV, de la Cruz J; RNA. 2004;10:1073-1083. PMID:15208443

2: Npa1p, a component of very early pre-60S ribosomal particles, associates with a subset of small nucleolar RNPs required for peptidyl transferase center modification. Dez C, Froment C, Noaillac-Depeyre J, Monsarrat B, Caizergues-Ferrer M, Henry Y; Mol Cell Biol. 2004;24:6324-6337. PMID:15226434