An Experimental Approach to the Study of AG-NOR Proteins.

Abstract

Purified polyclonal antibodies have been obtained against 100 KD and 36 KD Ag-NOR proteins. These two antibodies have been used to study the immunolocalization of both proteins on different cell types subjected to various conditions of cell activity and to observe a nucleolar labelling with anti-36 kDa Ag-NOR protein antibody evenly distributed over the dense fibrillar component and granular component, and with anti-100 kDa mainly localized to the dense fibrillar component. After actinomycin D treatment, immunolabelling with both antibodies was found restricted to the granular zone of segregated nucleoli. Moreover, to further study the functional role of these proteins, we have used an electroporation system to introduce both antibodies into the nuclei of living cells, and have clearly detected a different nucleolar behaviour.The combination of these techniques has been shown to be an important tool to deepen the knowledge of the nucleolus and has allowed us to propose that the difference in nucleolar localization of the major 36 kDa and 100 kDa Ag-NOR proteins is the consequence of a different role of both proteins in the synthesis and processing of rRNA.

The phosphoprotein pp135 is an essential constituent of the fibrillar components of nucleoli and of coiled bodies

“…Several AgNOR proteins have been identified on gels and western blots (Olson 1990). However, the best known AgNOR proteins (i.e., nucleolin/C23 and B23) have never been reported to be present either in the mitotic NOR, in the fibrillar centers or in the CBs but, rather, in the dense fibrillar component and in the granular component, which is not a silver-stainable structure of nucleoli (Biggiogera et al 1989;Escande-Geraud et al 1985;Ochs et al 1983Ochs et al , 1985Rodrigo et al 1994;Spector et al 1984;Weisenberger and Scheer 1995). pp135 is, on the other hand, known to exhibit a very high affinity for silver and Giemsa staining (Pfeifle et al 1986).…”