Figure 3.

A summary of the changes occurring in the cell nucleus when CpG methylation is prevented or inhibited. On the left the meCpG positive cells maintain a stringent compartmentalization of RPI and RPII transcription, the former in the nucleolus (light blue) on the rRNA genes, the latter in the nucleoplasm (dark blue). Loss of CpG methylation increases the number of active rRNA genes, but not the number of RPI (green) transcription complexes, and allows the incursion of RPII (red) and the production of aberrant RNA transcripts. The rRNA genes are normally densely occupied by RPI transcription complexes and this acts to exclude RPII, while the increase in the number of active rRNA genes after loss of DNA methylation reduces the density of RPI complexes and allows access to RPII with consequent effects on rRNA processing and ribosome biogenesis.