Human and rodent 18 S rRNA contain about 38 pseudouridine residues. By correlating RNA oligonucleotide data with complete sequence data derived from ribosomal DNA, 30 pseudouridine residues can be located in the RNA sequence, either exactly or to within two or three residues. Pseudouridine and 2′-O-methyl groups are interspersed throughout mammalian 18 S rRNA, but not in closely parallel fashion. Whereas the largest cluster of 2′-O-methyl groups is in the 5′ one-third of the molecule, the greatest concentration of pseudouridine is in the central one-third of the molecule.
