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We used electron spectroscopic imaging to map nucleoplasmic transcription sites in human cells at unprecedented resolution. HeLa cells were permeabilised, nascent transcripts were extended in BrUTP by approximately 40 nucleotides and the resulting BrRNA immunolabelled with gold particles before structures were viewed. Nascent RNA is almost invariably associated with polymorphic and nitrogen-rich (but phosphorus-poor) structures with a diameter of approximately 87 nm and mass of 10 MDa (calculated by reference to nucleosomes with known numbers of phosphorus and nitrogen atoms). Structures with similar atomic signatures and diameters were observed using correlative microscopy and in unpermeabilised cells. Our results are consistent with RNA synthesis occurring on the surface of these huge protein-rich transcription factories.

Original publication




Journal article


J Cell Sci

Publication Date





1999 - 2007


Binding Sites, DNA, HeLa Cells, Humans, Microscopy, Energy-Filtering Transmission Electron, Nucleosomes, Protein Binding, RNA, RNA Polymerase II, Structure-Activity Relationship, Transcription, Genetic, Uridine Triphosphate