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

Figure 2.

Figure 2.

UBF depletion results in loss of NOR competency. The top cartoon indicates the features of human NORs, including an array of rDNA repeats (red), surrounded by a conserved distal junction (DJ, green) and proximal junction (PJ, white). Each rDNA repeat is comprised of a transcription unit and an intergenic spacer (IGS). The DJ and PJ were named in regard to their positions relative to the centromere. Competent NORs appear as 2° constrictions, gaps in DAPI staining (blue), on metaphase chromosome (middle left) and participate in nucleolar formation in interphase (bottom left). Interestingly, DJ sequences appear as foci localized within perinucleolar heterochromatin. DJ foci identify individual NORs and indicate that mature nucleoli are comprised of multiple NORs. Note, the association of neo-NORs with endogenous human NORs has revealed the existence of NOR territories, indicated by a dashed white line (bottom left), within mature nucleoli. Upon UBF depletion, a subset of competent NORs loses UBF and become silenced. Consequently, they fail to form 2° constrictions during mitosis (middle right) and fail to participate in nucleolar formation in interphase (bottom right).