Concentration of particular high molecular mass phosphoproteins in rat liver nuclei and nuclear matrix decreases following inhibition of RNA synthesis by alpha-amanitin.

Purified liver nuclei were isolated from rats treated with non-lethal doses of alpha-amanitin, actinomycin D, galactosamine or cycloheximide. The nuclei were incubated in the presence of adenosine 5'-[gamma-32P]triphosphate, and digested with DNAase or DNAase plus high salt concentrations to prepare nuclear residual structures. Using SDS-polyacrylamide gel electrophoresis followed by autoradiography, samples from untreated rats were shown to contain major phosphoproteins in the range 76-260 kDa, with a prominent triplet of bands with 110, 117 and 128 kDa. Treatment of animals with alpha-amanitin or high doses of actinomycin D and galactosamine caused a significant decrease in the concentration of a few phosphorylated species, including the 110 kDa protein in whole nuclei, and their disappearance from the nuclear matrix or residual ribonucleoprotein structures after 1-3 h. The changes were reversible, complete recovery being observed after 5 h in the case of alpha-amanitin. No similar results were obtained with nuclei from rats treated with the translation inhibitor cycloheximide. The data are discussed in view of a possible effect of certain high molecular mass phosphoproteins on reactions of the heterogeneous nuclear RNA/mRNA pathway in the cell.