[Action of actinomycin D on the nucleolar function and ultrastructure of a pig embryo kidney cell culture].

It has been shown that the morphofunctional alterations of nucleoli in KEPV cells induced by actinomycin D at 0,05 microgram/ml proceed in two steps. During the first 3 h of actinomycin D action a level of the RNA synthesis in nucleoli falls to 25% from the initial one. Simultaneously the following morphological alterations take place: condensation of the chromatin, infiltration of nucleoli, displacement to outlining regions, increase of the dimensions and reduction of number of fibrillar centres, gradual disappearance of compact fibrillar zone and appearance looplike granular structures. During the following 3-6 h of antibiotic action the RNA synthesis falls slightly, nucleoli dimensions decrease, fibrillar micronucleoli appear.