A nucleosome core is transferred out of the path of a transcribing polymerase.

We have determined the fate of a nucleosome core on transcription. A nucleosome core was assembled on a short DNA fragment and ligated into a plasmid containing a promoter and terminators for SP6 RNA polymerase. The nucleosome core was stable in the absence of transcription. The distribution of nucleosome cores after transcription was examined. The histone octamer was displaced from its original site and reformed a nucleosome core at a new site within the same plasmid molecule, with some preference for the untranscribed region behind the promoter. These observations eliminate several models that have been proposed for transcription through a nucleosome core. Our results suggest that a nucleosome core in the path of a transcribing polymerase is displaced by transfer to the closest acceptor DNA.