Incorporation of 6-thioguanosine and 4-thiouridine into RNA. Application to isolation of newly synthesised RNA by affinity chromatography.

Isolation of newly synthesised RNA can be achieved by treatment of 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. On the other hand, even after long exposure to high concentrations of 4-thiouridine, the syntheses of RNA and protein are not significantly affected. Proteins synthesised after treatment of cells with 6-thioguanosine are less stable than proteins synthesised after treatment of cells with 4-thiouridine.