Quantitation and potential function of nucleolar phosphoprotein pp 105 in mouse tumor cells, embryonic cells and normal tissues

1. Nucleolar phosphoprotein pp 105 was determined in various mouse cell and tissue extracts using a highly sensitive ELISA. The results indicate that the highest relative amounts of pp 105 correlate with cells and tissues of high growth rate such as tumor cell lines, solid tumors and embryonic tissues. 2. The specific phosphorylation of pp 105 was compared in a 1 min endogenous phosphorylation assay with native cell and tissue extracts. 3. The mitogenic activity of highly purified pp 105 was demonstrated in cultures of resting mouse embryonic cells and mouse thymocytes.