Transcription of open and covered promoters

(a) Open promoters have a nucleosome-depleted region (NDR) and no TATA box. Activator proteins (ACT) are attracted to enhancer sequences (ES) to recruit RNA polymerase II for transcription. (b) With covered promoters, transcription is activated by activator-protein binding and displacement of nucleosomes. Closed chromatin  is inaccessible to transcription factors and insensitive to DNase I digestion, whereas following activator binding and nucleosome displacement, the resulting open chromatin binds transcription factors and is DNase I hypersensitive(a) Open promoters have a nucleosome-depleted region (NDR) and no TATA box. Activator proteins (ACT) are attracted to enhancer sequences (ES) to recruit RNA polymerase II for transcription. (b) With covered promoters, transcription is activated by activator-protein binding and displacement of nucleosomes. Closed chromatin  is inaccessible to transcription factors and insensitive to DNase I digestion, whereas following activator binding and nucleosome displacement, the resulting open chromatin binds transcription factors and is DNase I hypersensitive

(a) Open promoter —2 nudeosome -1 nudeosome +1 nudeosome +2 nudeosome Poly A/l' tract (no TATA box) (b) Covered promoter 0 Closed chromatin {DNase i insensitive and transcriptionally silent i Nucleosome Promoter Gene Enhancer start site 9 Activator binding in progress I +1 nudeosome +2 nudeosome additional bindinhg 6 Open chromatin Chromatin remodeling and l displacement I Nucleosomes are displaced: and activator binds. i Activator binding i -0 - to ‘ RNA pol II and transcription DNase I hypersensitivity factors bind promoter. detected following nudeosome displacement if RNA pol ll Persistent DNase I hypersensitivity Transcription is initiated.