Phosphoproteins crosslinked to poly(A) + heterogeneous nuclear RNA after irradiation with ultraviolet light

Isolated liver nuclei or whole lymph node lymphocytes stimulated with concanavalin A in culture were irradiated with ultraviolet light. The crosslinked structures of poly(A)+ heterogeneous nuclear RNA and protein were purified on oligo(dT)-cellulose after labelling irradiated nuclei in the presence of adenosine 5'-[gamma-32P]triphosphate and analysed by SDS-polyacrylamide gel electrophoresis. The liver and lymphocyte nuclear proteins included about 17-19 species of 35-150 kDa and were shown to produce quite similar electrophoretic band patterns. Two proteins of 110-120 and 40-42 kDa were phosphorylated. Using partial proteolytic digestion the large-size crosslinked phosphoprotein has been identified as the 110 kDa component described previously (Schweiger, A. and Kostka, G. (1984) Biochim. Biophys. Acta 782, 262-268). The 40-42 kDa band was presumably related to the group C species of main proteins associated with heterogeneous nuclear RNA. In crosslinked nuclear structures from rats treated with low doses of alpha-amanitin for 1 h the relative amount of the 110-120 kDa phosphoprotein was reduced while the labelling with [32P]ATP was almost abolished.