Ultrastructural investigation of the effect of DNA, RNA, and protein synthesis inhibitors on ribosome crystallization

Abstract

Chick embryo fibroblast cultures have been submitted to a rapid cooling treatment in order to induce ribosome crystallization. This treatment induces the appearance of small and rare ribosome crystals in only a very low percentage of the interphasic cells. In order to investigate the metabolic conditions for the formation of ribosome crystals, the cultures have been exposed to some drugs inhibiting DNA, RNA, and protein synthesis before and during the rapid cooling treatment. The action of the following drugs was tested: mitomycin C, actinomycin D, puromycin, and cycloheximide. These drugs have been used also before and during the exposure of the cultures to high doses of vinblastine sulfate, which induces the appearance of a large quantity of ribosome crystals in almost all the cells. It has been observed that after actinomycin D and puromycin, ribosome crystals appear in a very high percentage of cells in comparison with the controls, even if variations in the number and dimensions of the ribosome crystals within each cell can be observed depending on the drug. Mitomycin C does not affect the ribosome crystal formation, while cycloheximide prevents it almost completely. The combined action of the metabolic inhibitors and VLB, moreover, has shown that no drug can completely prevent the formation of ribosome crystals in VLB-treated cells. The data of the paper partly confirm some of the hypotheses previously advanced for explaining the formation of ribosome crystals. Furthermore, they suggest that other metabolic conditions can be involved in this phenomenon.