Methylation activity was determined by reverse transcription under limited nucleotide and enzyme concentrations (28) as described previously (24). A total of 8 μg RNA was annealed to 32P-, 5΄-end labelled primer and then incubated with M-MLV reverse transcriptase (40 u, Promega), 2 μl 5xRT buffer, 0.25 μl superasin and 1.25 mmol dNTP's. The reactions were separated on either a 6 or 8% polyacrylamide/7 M urea gel and then visualised using a phosphorimager. Primers used for mapping were Map1316 (5΄-TAGTCCCTCTAAGAAGTGGATAACC-3΄) and Map13 (5΄-CTAGATAGTAGATAGGGACAGTGG-3΄). To determine the expression of snoRNAs, Northern blot analysis was performed with the following probes snR13 (5΄-CCACACCGTTACTGATTTGGCAAAA GC-3΄), snR5 (5΄-TAAGCATGGTAATCCGGAAGATC-3΄), snR87 (5΄-TAGAACATGGCGGTGTTCCAA GTGAT-3΄), artificial snoRNA (5΄-AATTGCGATAACGCTAGCTACATC-3΄) and 5S rRNA (5΄-CTACTCGGTCAGGCTC-3΄) as described previously (24). In some cases, methylene blue staining of 5S rRNA was used to check for equal loading.