Composition of hnRNA-associated proteins in rat liver is specifically altered after cycloheximide treatment.

Rats were treated with non-lethal doses of alpha-amanitin or cycloheximide. Nuclei were prepared and the particles carrying heterogeneous nuclear RNA (30--40 S-particles) isolated by density gradient centrifugation. In the case of alpha-amanitin the yield of particles was reduced to about 45%. Cycloheximide affected the composition of proteins associated with the nuclear RNA. In particular, the concentration of a 110 000 molecular weight protein as determined by sodium dodecylsulfate gel electrophoresis was reduced to 20--30% after 2 h and then increased to 150--180% of the control before it approached the normal level after 30 h. Possible mechanisms underlying these changes are discussed.