The nuclear DEAD box RNA helicase p68 interacts with the nucleolar proteinfibrillarin and colocalizes specifically in nascent nucleoli during telophase

The DEAD box protein, p68, is an established RNA-dependent ATPase and RNA h elicase in vitro, but neither the physiological function of this protein no r the macromolecules with which it interacts are known. Using a yeast two-h ybrid screen, we identified the nucleolar protein, fibrillarin, as a protei n that interacts with p68. Coimmunoprecipitation experiments confirmed that p68 and fibrillarin can form complexes in cellular extracts, and deletion analysis identified regions in each protein responsible for mediating the i nteraction. Immunofluorescence studies using confocal microscopy revealed t hat, in interphase cells, while fibrillarin is predominantly nucleolar, p68 shows a diffuse granular nuclear staining but is largely excluded from the nucleoli. Strikingly, both proteins colocalize in nascent nucleoli during late telophase. These data are consistent with a role for p68 either in pos tmitotic nucleolar reassembly or in the activation of ribosomal DNA transcr iption/preribosomal RNA processing during telophase and suggest that differ ential subnuclear compartmentalization mag be a mechanism by which interact ion of p68 with fibrillarin is regulated in the cell. (C) 2000 Academic Pre ss.