UHRF1 and malignant colon neoplasm: UHRF1 ubiquitin ligase activity was needed to support DNA methylation maintenance in low CpG density regions of the genome in both HCT116 and RKO colon cancer cell lines (Figure 4E–H and Supplementary Figure S4D–F), consistent with the hypothesis of histone ubiquitination functioning as a bookmark for low-density CpG methylation.