Syntheses of rRNA, 5.8S, 5S and tRNA are inhibited equally by 8-methoxypsoralen phototreatment ofTetrahymena thermophila

Abstract

Treatment of the ciliated protozoan Tetrahymena thermophila with 8-methoxypsoralen combined with long wavelength ultraviolet irradiation (tWA, X 360 nm) resulted in a dose dependent equal inhibition of the synthesis of rRNA, 5.8S, 5S and tRNA. Similar results were obtained with 3-carbethoxy-8-methylpsoralen which predominantly forms DNA mono-adducts. In contrast the synthesis of tRNA in T. thermophila was much less sensitive than that of rRNA, 5.8S and 5S RNA to treatment with short wavelength ultraviolet irradiation (UVB, X -254 nm). These results are interpreted in favor of a mechanism by which psoralen-DNA adducts (crosslinks >> monoadducts) inhibit RNA transcription initiation (in contrast to UVB which causes premature chain termination). Furthermore it is argued that RNA synthesis is regulated in equally sized domains regardless of the gene-size.

The Effects of DNA Covalent Adducts on in Vitro Transcription

“…These findings point to the importance of RNA synthesis inhibition in the mechanism of cytotoxicity of anticancer drugs. For nitracrine congeners, a close relationship between adduct-dependent inhibition of in vitro transcription and their cytotoxic effects has been observed. ,− It has been suggested that arrest in G 2 phase of the cell cycle by cisplatin is due to the inability of the cells to transcribe genes for mitosis. , Cisplatin is indeed a strong barrier for RNA pol 44 and, to lower extent, for DNA pol, ,175a while frequent bypasses of its ineffective isomer, trans -DDP, adducts are observed. , Actually a recent comparison of the effect of the two isomers on transcription in the cell is consistent with the studies at the subcellular level . These findings may provide a molecular basis for the different pharmacological properties of these stereoisomers.…”

Psoralen covalently linked to oligodeoxyribonucleotides: synthesis, sequence specific recognition of DNA and photo-cross-linking to pyrimidine residues of DNA

“…The covalent bonds of the psoralen-nucleic acid linkage are photoreversible by irradiation at 254nm (9). Psoralen modified DNA is used in the elucidation of nucleic acid structure and nucleic acid/protein interactions (10,11).…”