Effect of anthracycline antitumor antibiotics (adriamycin and nogalamycin) and cycloheximide on the biosynthesis and processing of major UsnRNAs.

In the present study, anthracycline antitumor antibiotics (e.g. adriamycin and nogalamycin), the potent RNA synthesis inhibitors and cycloheximide, the protein synthesis inhibitor, have been used to understand the events of biosynthesis and processing of major UsnRNAs (U1-U6). The anthracyclines inhibit the UsnRNAs biosynthesis (in terms of labelling) differentially in a dose dependent manner. The inhibitory effect of adriamycin and nogalamycin reached plateau at a concentration of 2.5 micrograms/ 10(6) cells/ml and 0.1 microgram/10(6) cells/ml respectively and indicates that nogalamycin is more inhibitory than adriamycin. The inhibition of the UsnRNAs synthesis (in terms of labelling) became maximum within 30 min of incubation and remained unaltered even after 2 h. Thus, it shows that the anthracyclines preferentially inhibit the initiation of the UsnRNA genes' transcription as it has been seen in cases of other large RNAs' synthesis by some other laboratories. The higher inhibitory effect of the anthracyclines on the biosynthesis of U5 and U6 compared to other UsnRNAs indicates the presence of more binding sites on the U5 and U6 snRNA genes. In presence of the anthracyclines, there was high retention of cytoplasmic major pre-UsnRNAs/ UsnRNAs which indicates that the elongation of the UsnRNA synthesis is probably impaired along with initiation; because for the proper processing of the pre-UsnRNAs, formation of the correct secondary structure of that pre-UsnRNA is necessary. Cycloheximide showed some differential effect on the pol II transcribed UsnRNAs (U1-U5) biosynthesis (in terms of labelling) however it has no effect on the pol III transcribed U6 snRNA. It implies that in the pol II transcribed UsnRNAs, some transacting labile factors, either activator or inhibitor, are involved. Whereas, the processing of the UsnRNAs (either pol II or pol III transcribed) was affected more or less in a similar fashion in presence of cycloheximide, indicating the involvement of some transacting labile factors in this event.