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

8-Methoxypsoralen DNA interstrand cross-linking of the ribosomal RNA genes in Tetrahymena thermophila. Distribution, repair and effect on rRNA synthesis

The distribution and repair of 8-methoxypsoralen-DNA interstrand cross-links in the ribosomal RNA genes (rDNA) in Tetrahymena thermophila have been studied in vivo by Southern blot analysis. It is found that the cross-links at a density of < or = 1/2 x 10(4) base pairs (bp) are distributed equally between three domains (terminal spacer, transcribed region and central spacer) as defined by restriction enzyme analysis (BamHI and ClaI). It is furthermore shown that a dosage resulting in approximately one cross-link per rDNA molecule (21 kbp, two genes) is sufficient to block RNA synthesis. Finally, it is shown that the cross-links in the rDNA molecules are repaired at equal rate in all three domains within 24 h and that RNA synthesis is partly restored during this repair period. The majority of the cells also go through one to two cell divisions in this period but do not survive.

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

The psoralen derivative 4,5',8-trimethylpsoralen was covalently linked to the 5'-terminus of an 18mer oligodeoxyribonucleotide in the course of solid phase synthesis using phosphoroamidite chemistry. The derivative was introduced as a phosphitylation compound in the last cycle of the oligomer synthesis. The reagent was prepared by 4'-chloromethylation of 4,5',8-trimethylpsoralen, introduction of a linker by ethanediol and phosphitylation with chloro-[(beta-cyanoethoxy)-N,N-diisopropylamino]-phosphine. After oxydation and deprotection the 5'-psoralen modified oligodeoxyribonucleotide was characterised by HPLC. Hybridisation of the psoralen-modified oligomer to a complementary single stranded 21mer followed by irradiation at 350 nm revealed a photo-cross-linked double-stranded DNA fragment analysed on denaturing polyacrylamide gels. The cross-link could be reversed upon irradiation at 254nm.