RNA is synthesized at the nuclear cage

The photomicrographs of ‘genes in action’ taken by Miller and colleagues strikingly illustrate transcription of eukaryotic genes by RNA polymerase moving along the DNA 1,2 . Although completed transcripts may be associated with sub-nuclear structures 3–7 , the view that a mobile polymerase processes along the DNA remains unchallenged. Here we examine an alternative view—that transcription occurs as DNA passes through a transcription complex fixed to a sub-nuclear structure, and we show that transcribed sequences are closely associated with a sub-nuclear structure that we call a nuclear cage.