MBIO 4612 Lecture 16: Eukaryotes Lecture 16
9 Feb 2020
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Eukaryotes Lecture 16
About 10% of euk DNA is
sensitive to DNaseI
DNase I Hypersensitivity
Least to most sensitive:
- Non-transcribed DNA → actively transcribed DNA → naked DNA
Adjacent to & within transcribed regions of chromatin, there are small regions that are almost as
sensitive as naked DNA!
DNase I hypersensitive sites → occur where TFs are bound
- From cleavage by DNase I at sites immediately adjacent to bound TFs
o Binding of at least SOME regulatory factors to DNA results in exclusion of
nucleosomes in the immediate area
- Suggests that TFs may promote transcription by competing with histones for binding of
DNA
Other restriction enzymes (besides DNase I) have been used to map hypersensitive sites
- Experiment → restriction enzyme hypersensitivity analysis for chromatin of the MMTV
promoter. Promoter respone to transcriptional
activation by glucocorticoid receptor (GR) by
glucocorticoid (Dex)
▪ GR is a TF regulated by Dex
o MMTV = murine retrovirus → integrates
into the genome & is compacted into
normal chromatin
- Results:
o Without Dex = MMTV promoter is not
transcribed (compacted into chromatin)
o With Dex = transcription is induced,
access of restriction endonucleases to
MMTV chromatin is enhanced
(hypersensitive)
o See bands in both + and – in Hae III →
restriction site is in between
nucleosomes, this is linker DNA! Already
Document Summary
About 10% of euk dna is sensitive to dnasei. Non-transcribed dna actively transcribed dna naked dna. Adjacent to & within transcribed regions of chromatin, there are small regions that are almost as sensitive as naked dna! Dnase i hypersensitive sites occur where tfs are bound. From cleavage by dnase i at sites immediately adjacent to bound tfs: binding of at least some regulatory factors to dna results in exclusion of nucleosomes in the immediate area. Suggests that tfs may promote transcription by competing with histones for binding of. Other restriction enzymes (besides dnase i) have been used to map hypersensitive sites. Experiment restriction enzyme hypersensitivity analysis for chromatin of the mmtv promoter. Promoter respone to transcriptional activation by glucocorticoid receptor (gr) by glucocorticoid (dex: gr is a tf regulated by dex, mmtv = murine retrovirus integrates into the genome & is compacted into normal chromatin.
