( Human Reproductive Engineering Institute, Central South University Xiangya Medical School, Changsha 410078, China )

Abstract Ribose methylation is a widespread type of nucleotide modification in rRNA. In order to map the methylation sites of rice 25 S rRNA, a series of primers complementary to both yeast 28 S and rice 25 S rRNA simultaneously were synthesized. Primer extensions at different dNTP concentrations were carried out to detect the methylation sites of both yeast and rice rRNAs. The data showed that over 80% of the methylation sites in yeast 28 S rRNA was also detected in rice. In addition, compared with the known methylation sites of Arabidopsis 25 S rRNA, other 54 sites probably methylated in rice were found in Arabidopsis. Thus, there are 85 methylation sites detected altogether; the distribution of the methyl sites in rice 25 S rRNA was determined. The results show that most of the sites are conserved among different species, especially between closely related species. And remarkably, there are much more ribose methylation sites in plant rRNA, and the propinquous methylation sites in plants are more frequent than those in other eukaryotes. Moreover, the data provide the most important clue for searching new box C/D snoRNAs.