Methylation map of Xenopus laevis ribosomal RNA.

One of the most enigmatic features of eukaryotic ribosomal RNA is the presence of many methylated nucleotides. The numbers of RNA methyl groups range from approximately 70 per ribosome in yeast to over 100 in vertebrates. Here it is shown that the methylated nucleotides in Xenopus laevis rRNA are broadly but non-uniformly distributed. In 18S rRNA 2'-O-methylations are partly concentrated in the 5' region and base methylations near the 3' end. In 28S rRNA methyl groups are infrequent in the 5' region, moderately frequent in the central region and abundant in an 1,100-nucleotide tract near the 3' end.