Dispersed rRNA genes clustered in a single perinuclear nucleolus (B) Immunofluorescence analysis using antibodies against the nucleolar protein PfNop1 (red) combined with DNA FISH (green) for individual rRNA genes (A1, A2, S1, S2, and 5S) and a subtelomeric unrelated gene (PFD0110w) on chromosome 4. In the human malaria parasite Plasmodium falciparum, rDNA is not arranged in tandem arrays; instead, single rDNA units (18S–5.8S–28S) are spread out on different chromosomes (chromosomes 1, 5, 7, 11, and 13). rDNA units from different chromosomes cluster in a single perinuclear nucleolus, regardless of their transcriptional status. This clustering of rRNA genes was observed only in prereplicative parasite blood stages.

Schematic recapitulating nucleolar clustering of dispersed rRNA genes and the

nucleolus-associated telomeric cluster

Mancio-Silva L, Zhang Q, Scheidig-Benatar C, Scherf A. Clustering of dispersed ribosomal DNA and its role in gene regulation and chromosome-end associations in malaria parasites. Proc Natl Acad Sci U S A. 2010 107(34):15117-22. PMID: 20696894