Alternative pre-rRNA processing pathways in human cells and their alteration by cycloheximide inhibition of protein synthesis

Eur J Biochem. 1993 Feb 15;212(1):211-5. doi: 10.1111/j.1432-1033.1993.tb17652.x.


rRNA processing pathways in humans have been reinvestigated through systematic Northern-blot hybridizations of HeLa cell nuclear RNA with a collection of digoxigenin-labeled rDNA probes from different regions of the human rDNA transcriptional unit. In addition to the known 45S, 41S, 32S and 21S pre-rRNA, two major pre-rRNA fractions were identified; a '30S' (about 5800 nucleotides) precursor to 18S rRNA containing an external transcribed spacer at the 5' end (ETS) and internal transcribed spacer (ITS) 1 sequences and a '12S' (about 950 nucleotides) precursor to 5.8S rRNA containing ITS 2 sequences. These pre-rRNA species do not react with probes located near the 3'-terminal segments of ITS 1 or ITS 2, thus suggesting that processive endonuclease cuts occur within ITS spacer sequences. The simultaneous occurrence of at least two alternative 45S pre-rRNA processing pathways is deduced, which correspond to a different temporal order of endonuclease attack at the sites located near the 5' end of 18S rRNA and within ITS 1. In-vivo labeling experiments with [14C]uridine revealed that inhibition of protein synthesis with cycloheximide abolishes the endonuclease cut at the 5' end of 18S rRNA and the formation of 41S pre-rRNA, while the cut within ITS 1 and the processing to 32S and '30S' pre-rRNA remains relatively unaltered.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Blotting, Northern
  • Cycloheximide / pharmacology*
  • HeLa Cells
  • Humans
  • Molecular Sequence Data
  • Protein Biosynthesis
  • RNA Precursors / metabolism*
  • RNA Processing, Post-Transcriptional / drug effects*
  • RNA, Ribosomal / metabolism*


  • RNA Precursors
  • RNA, Ribosomal
  • Cycloheximide