AgNOR proteins from morphologically intact isolated nucleoli

AgNOR staining has been proposed as a useful tool for the diagnosis and pro gnosis of cancer. The AgNOR proteins, however, have not yet been clearly id entified and characterized, possibly due to the partial character of the re sults obtained when studying the proteins extracted from altered nucleoli i solated by "standard" methods. In the present study, we analysed, on wester n blots, the AgNOR staining profiles obtained with protein extracts from Eh rlich tumor cell nucleoli isolated by a recent procedure that preserves the nucleolar ultrastructure. In addition to the well-known C23 and B23 protei n bands, we readily detected an extra band at approximately 125 Kda. By imm unoblotting, we showed that this polypeptide may be related to the nucleola r phosphoprotein pp135 evidenced in rat-cell nucleoli. By irnmunoelectron m icroscopy, we detected this protein in the dense fibrillar component and fi brillar center of the nucleoli as well. as the coiled bodies. The distribut ion coincides with the cytochemical AgNOR staining pattern obtained at the ultrastructural level.