Proteins H/ACA Small Nucleolar RNA-Associated Rnt1p Is Required for the Nuclear Import of A Physical Interaction between Gar1p and

, the double-stranded RNA nuclease Rnt1p andthe H/ACA snoRNA pseudouridylase complex participate in the transformation of the nascent pre-rRNAtranscript into 35S pre-rRNA. Here we demonstrate the binding of a component of the H/ACA complex (Gar1p)to Rnt1p in vivo and in vitro in the absence of other factors. In vitro, Rnt1p binding to Gar1p is mutuallyexclusive of its RNA binding and cleavage activities. Mutations in Rnt1p that disrupt Gar1p binding do notinhibit RNA cleavage in vitro but slow RNA processing, prevent nucleolar localization of H/ACA snoRNA-associated proteins, and reduce pre-rRNA pseudouridylation in vivo. These results demonstrate colocalizationof various components of the rRNA maturation complex and suggest a mechanism that links rRNA pseudouri-dylation and cleavage factors.