Zinc ions are differentially required for the transcription of ribosomal 5S RNA and tRNA in a HeLa-cell extract.
Chelation of divalent cations by 5 mM EDTA and subsequent removal by dialysis from a cytoplasmic HeLa cell extract leads to a complete loss of 5S rRNA transcription without affecting tRNA synthesis. Transcription complexes for 5S RNA can no longer be assembled in such a zinc-depleted extract and this ability can be fully restored only by the re-addition of 5 microM zinc. Reconstitution experiments with isolated protein fractions show that transcription factor A from HeLa-cells requires zinc to exert its specific function. Pre-formation of transcription complexes partially protects the metal ion against removal by chelation even in the presence of 1.8 M KCl. These results indicate that the zinc ions are bound to mammalian transcription factor IIIA which, in a transcription complex, binds very strongly to the 5S RNA gene. Cation depletion with 75 mM EDTA also suppresses tRNA transcription; an effect which is reversible by zinc addition. We conclude that beside for the binding of TF IIIA, zinc is also bound with a different affinity to a transcription component common to 5S and tRNA synthesis, most likely polymerase III itself.
D004492:Edetic Acid / Q000494:pharmacology; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D012335:RNA, Ribosomal / Q000235:genetics*; D012343:RNA, Transfer / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects*; D015032:Zinc / Q000494:pharmacology*
D012335:RNA, Ribosomal; D012343:RNA, Transfer; D004492:Edetic Acid; D015032:Zinc