Localization of phosphoprotein PP 105 in cell lines of various species

The cellular location of phosphoprotein pp 105 was determined in various mouse cell lines with rabbit anti mouse pp 105 serum. Immunofluorescence was predominantly observed in the nucleoli in addition to a diffuse but weaker fluorescence of the whole nucleus. Cell surface fluorescence was obtained only with cells grown in suspension cultures. The presence of pp 105 in normal mouse tissue was demonstrated with tissue extracts by immunobinding assays. Cross-reacting phosphoproteins with the same molecular weight were detected in hamster and human cell lines as well as in chicken cartilage cells and Drosophila embryonic cells. Endogenous phosphorylation of pp 105 studied with purified mouse nucleoli showed optimal activity at isotonicity, pH 8.7, in the presence of 10 mM magnesium.