A nonribosomal landscape in the nucleolus revealed by the stem cell protein nucleostemin.

Nucleostemin is a p53-interactive cell cycle progression factor that shuttles between the nucleolus and nucleoplasm, but it has no known involvement in ribosome synthesis. We found the dynamic properties of nucleostemin differed strikingly from fibrillarin (a protein directly involved in rRNA processing) both in response to rRNA transcription inhibition and in the schedule of reentry into daughter nuclei and the nucleolus during late telophase/early G1. Furthermore, nucleostemin was excluded from the nucleolar domains in which ribosomes are born--the fibrillar centers and dense fibrillar component.