Removal of pectins from methylated rRNA and precursors by LiCl

The methyl group of radioactive methylmethionine is incorporated preferentially into pectin, a methylated polysaccharide, which massively contaminates RNA preparations. This makes it difficult to discern the methylated RNA species of growing tissues of higher plants. A method for the extraction of pectic substances from RNA preparations of plants is described. Ethanol precipitates containing RNA are suspended in 2m lithium chloride (LiCl) and the pectin is removed with the supernatant after centrifugation. LiCl purification of RNA from Vicia faba root meristems allows the direct identification on polyacrylamide gels of methylated RNA species labeled with ³H]methyl methionine. Presumpive precursors of rRNA which fall into the range of apparent molecular weights of 2.7–2.9, 2.2–2.4, 1.4–1.5, and 0.72–0.75 × 10⁶ are shown to be methylated, in addition to the methylation of the fully processed rRNAs of MW 1.3 and 0.7 × 10⁶.