rRNA promoter methylation by sodium bisulfite sequencing. DNA samples derived from CD34⁺ healthy subjects and MDS patients were treated with sodium bisulfite, PCR amplified, cloned, and sequenced. Each row represents an individual clone. The open squares represent unmethylated CpGs, closed squares represent methylated CpGs, and gray squares indicate that data were not obtained. One of the CpGs (CpG 6 in Figure 2) reported in the published rDNA sequence (accession number U13369) was found to be missing when individual clones were sequenced.