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. Author manuscript; available in PMC: 2021 Oct 2.
Published in final edited form as: Trends Genet. 2019 Aug 22;35(10):710–723. doi: 10.1016/j.tig.2019.07.011

Figure 1. Organization of the nucleolus organizer region (NOR) and the rDNA array.

Figure 1.

Structure of the rDNA array; IGS = non-transcribed intergenic spacer. Proximal (PJ) and distal (DJ) junction link the rDNA array to the neighboring genomic region. NORs reside in 5 human chromosomes and are structurally complex rather than neatly organized as shown above: repeat units can be truncated, inverted, and contain small and large indels. NOR gives origin the nucleolus (black circle), a relatively large non-membrane bound organelle inside the cell nucleus. The colors represent chromatin from other chromosomes. A single nucleolus or multiple nucleoli can exist per cell.