MAPPING RNA REGIONS IN EUKARYOTIC RIBOSOMES THAT ARE ACCESSIBLE TO METHIDIUMPROPYL-EDTA-CENTER-DOT-FE(II) AND EDTA-CENTER-DOT-FE(II)

Methidiumpropyl-EDTA.Fe(II) [MPE.Fe(II)] and EDTA.Fe(II) were used to investigate the structure of Drosophila melanogaster ribosomes. Cleava ge reactions were performed on intact ribosomes in cell lysates in vit ro and analyzed by primer extension with reverse transcriptase using o ligodeoxynucleotide primers. Regions of 18S and 28S ribosomal RNAs (rR NAs) which are accessible to MPE.Fe(II) and EDTA.Fe(II) are located al most exclusively within expansion segments. The accessibility of these regions to cleavage indicates that they are likely exposed on the sur face of eukaryotic ribosomes. These results provide information about the overall tertiary structure of rRNA in ribosomes.