In eukaryotes, pre-rRNA processing depends on a large number of non-ribosomal trans-acting factors that form large and intriguingly organized complexes. A novel nucleolar protein, Nop53p, was isolated by using Nop17p as bait in the yeast two-hybrid system. Nop53p also interacts with a second nucleolar protein, Nip7p. A carbon source-conditional strain with the NOP53coding sequence under the control of theGAL1promoter did not grow in glucose-containing medium, showing the phenotype of an essential gene. .
