Analysis of pre-rRNAs in heat-shocked HeLa cells allows identification of the upstream termination site of human polymerase I transcription.

摘要: Human rRNA precursors from normal or stressed HeLa cells were studied by S1 nuclease mapping of unlabeled RNA and antisense RNase that had been labeled in vivo with (32P)PO/sub 4/. Heating to 43{sup 0}C decreased the amount newly synthesized less than 5% control level led greater 95% inhibition transcription termination at a region 355 362 nucleotides downstream 3' end 28S rRNA, readthrough continuing into next unit. 42{sup 60% this site; 50% transcripts extended nontranscribed spacer ended 200 210 upstream polymerase I (Pol I) initiation site. This is presumed be human site because absence RNAs 5' corresponding region, location relative Pol 1 (which similar terminators other species), fact it 15 25 sequence GGGTTGACC, which has an 8-of-9 base identify sequencemore » Surprisingly, treatment sodium arsenite, also leads induction stress response, did not inhibit termination. was same extent as termination, lends support hypothesis are coupled. Although almost completely inhibited 0}C, majority recently rRNAs processed have correct 28S. finding suggests 3'-end formation can involve endonucleolytic cut solely dependent on exonucleolytic trimming correctly terminated rRNAs.« less