title: Photobinding of 8-methoxypsoralen to transfer RNA and 5-fluorouracil-enriched transfer RNA.
abstract: The photobinding of [3H]8MOP to tRNA upon irradiation at 365 nm in the absence of O2 was determined by gel filtration. The maximum photobinding was found to be ca. 4 mol of 8MOP er mol of tRNA and 5FU-tRNA, with an overall quantum yield of 2.3 X 10(-3). The photobinding kinetics for 8MOP-tRNA showed an apparent induction period or sigmoidal kinetic curve, indicating a specific initial photobinding site on tRNA which was identified as 4-thiouridine at position 8 from the 5'-end of Escherichia coli tRNA. Photobinding of 8MOP to 5FU-tRNA proceeded without an apparent induction period. 8MOP-tRNA and 8MOP-5FU-tRNA adducts were characterized by absorption, fluorescence, and CD spectroscopy. A modified procedure was also developed to analyze the nucleoside composition in modified 8MOP-tRNA and 8MOP-5FU-tRNA. The results showed that 8MOP photochemically added mainly to pyrimidine bases. The photobinding of 8MOP changed the conformation (secondary in particular) of tRNA and inhibited aminoacyl-tRNA synthetase activity.
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism; D002942:Circular Dichroism; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000201:enzymology; D005472:Fluorouracil; D008730:Methoxsalen; D012343:RNA, Transfer / Q000378:metabolism / Q000528:radiation effects; D013050:Spectrometry, Fluorescence; D046249:Transfer RNA Aminoacylation; D014466:Ultraviolet Rays
chemical_list: D012343:RNA, Transfer; D000604:Amino Acyl-tRNA Synthetases; D005472:Fluorouracil; D008730:Methoxsalen