This family includes the Urb2 protein from yeast that are involved in ribosome biogenesis [1].

1: 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