NUCLEOSOMAL STRUCTURES OF C-MYC PROMOTERS WITH TRANSCRIPTIONALLY ENGAGED RNA-POLYMERASE-II

Organization of DNA into chromatin has been shown to contribute to a r epressed state of gene transcription. Disruption of nucleosomal struct ure is observed in response to gene induction, suggesting a model in w hich RNA polymerase II (pol II) is recruited to the promoter upon reor ganization of nucleosomes, Here we show that induction of c-myc transc ription correlates with the disruption of two nucleosomes in the upstr eam promoter region. This nucleosomal disruption, however, is not nece ssary for the binding of pol II to the promoter, Transcriptionally eng aged pol II complexes can be detected when the upstream chromatin is i n a more closed configuration. Thus, upstream chromatin opening is sug gested to affect activation of promoter-bound pol II rather than entry of polymerases into the promoter, Interestingly, pol II complexes are detectable in both sense and antisense transcriptional directions, bu t only complexes in the sense direction respond to activation signals resulting in processive transcription.