Fig. 3.

Sketch to compare morphology of transcription a in nucleoli and b in transcription factories. The transcription factory core (tf) is functionally related to the fibrillar center (fc), and transcription takes place at the surface of both entities. Active genes come into contact with the polymerases by chromatin loop formation out of silenced chromatin (gray dots). In nucleoli, nascent transcripts (brown) are predominately found in the dense fibrillar component (df) where RNA processing commences. A similar zone can be postulated for the transcription factory, Pol I…green dots, Pol II pink dots, gc granular component