Analysis of the Methylation Sites in Yeast Ribosomal RNA.

The methylation sites and the number of methyl groups of 26-S and 17-S ribosomal RNA (rRNA) of Saccharomyces carlsbergensis were investigated. 26-S and 17-S rRNA contain 43 and 24 methyl groups per molecule, respectively, of which in both molecules 6 are attached to the heterocyclic bases. In 26-S rRNA the base-methyl groups are present as two copies of m³U, m5C as well as m¹A, whereas the methylated bases in 17-SrRNA are one mTG, one methylated cytidine and two of m26A. In 17-S rRNA there are 11 different alkali-stable (i.e. ribose-methylated) dinucleotides, while 26-S rRNA contains 15 different alkali-stable dinucleotides, and in addition 4 alkali-stable trinucleotides (Am-Cm-Gp, Am-Gm-Cp, Am-Am-Up and Um-Gm-ψp). Most of the methylated oligonucleotides found in a ribonuclease T1 digest of 26-S or 17-S rRNA occur in approximately one-molar amounts. The combined data suggest that yeast ribosomal RNA is essentially homogeneous in its methylated sequences and in addition that the methylation is a highly specific process. [ABSTRACT FROM AUTHOR]