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. 2014 Oct 30;13(16):2501–2508. doi: 10.4161/15384101.2014.949124

Figure 1.

Figure 1.

Schematic representation of nucleolar compartmentalization. Top left diagram represents a nucleolus within a DAPI-stained nucleus (blue). Nucleoli are subdivided into FC (green), DFC (yellow) and GC (red). FCs constitute the core of nucleoli and are surrounded by DFCs. These compartments are embedded within the GC that is typically surrounded by perinucleolar heterochromatin (dark blue). rDNA transcription by the pol I transcription machinery (UBF, SL1, Rrn3 and pol I) occurs at the interface between FCs and DFCs (white box). The resulting 47 S pre-rRNA transcripts undergo a highly coordinated series of cleavages (green arrows) and modifications to generate the mature 18 S, 5.8 S and 28 S rRNA. Early processing events occur within the DFC (yellow box), while later processing events and assembly of ribosomal subunits occur within the GC (red box). Note that pseudo-NORs support the view that FCs are the interphase counterparts of the mitotic 2° constrictions and that they contain non-transcribed rDNA sequences and unengaged pol I machinery recruited in a UBF-dependent manner (green box).