Incorporation of 6‐Thioguanosine and 4‐Thiouridine into RNA

Abstract

Isolation of newly synthesized RNA can be achieved by treatment of [baby hamster kidney BHK-21/C 13] cells in culture with 6-thioguanosine or 4-thiouridine followed by separation of thiol-containing RNA by affinity chromatography on mercurated cellulose columns. After short periods of treatment with 6-thioguanosine the proportion of RNA retained on mercurated cellulose is the same for both poly(A)-containing and poly(A)-free RNA, indicating similar incorporation of the drug into mRNA and rRNA. However, after longer periods of exposure, the cytotoxic effect of 6-thioguanosine results in diminished incorporation of radioactive uridine into RNA and of radioactive leucine into protein. This suggests that synthesis of both RNA and protein are impaired. Conversely, even after long exposure to high concentrations of 4-thiouridine, the synthesis of RNA and protein are not significantly affected. Proteins synthesized after treatment of cells with 6-thioguanosine are less stable than proteins synthesized after treatment of cells with 4-thiouridine.