Secondary Structure Maps of RNA: Processing of HeLa Ribosomal RNA

Ribosomal RNA precursors and mature 28S ribosomal RNA from HeLa cells display a highly reproducible secondary structure of hairpin loops after they are spread and examined in an electron microscope. This structure was used to map the linear arrangement of these molecules. Partial digestion with 3'-exonuclease from ascites cell nuclei established that the 28S RNA region is located at the 5'-end of the 45S precursor. A spacer sequence follows the 28S region. This is followed by the 18S RNA region, and by another spacer sequence at the 3'-end. The 41S RNA contains both 18S and 28S regions. The 32S RNA contains only 28S RNA plus spacer, and the 20S RNA contains only 18S RNA plus spacer. Several minor nucleolar RNA components were also mapped with respect to the 45S RNA. These experiments lead to a more detailed processing pathway for HeLa ribosomal RNA which is in good agreement with earlier work.