The pseudouridine contents of the ribosomal ribonucleic acids of three vertebrate species. Numerical correspondence between pseudouridine residues and 2''-O-methyl groups is not always conserved.

The pseudouridine contents of the rRNA species of HeLa cells, mouse L-cells and Xenopus laevis cultured kidney cells were examined. Pseudouridine, like 2'-O-methylation, was found to occur relatively frequently in each of the high-molecular-weight rRNA species. However, the numerical data do not support the idea that there is a general one-to-one relationship between pseudoridine residues and 2'-O-methyl groups in vertebrate rRNA.