Chromatin - a general transcriptional repressor
- Created by: natasha8sherry
- Created on: 10-11-13 15:56
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- Chromatin - a general transcriptional repressor
- The N-terminal tails of histones are free to be modified to activate transcription
- Active chromatin is in different conformation to inactive
- Active regions sensitive to cleavage by DNase I - hyper DNase sensitive sites as are nucleosome free
- E.g. enhancer regions of genes ready for transcription
- E.g. globin gene locus in pre-erythroid cells is DNase sensitive in some cells but DNase resistant in others where globin is not transcribed
- Active regions sensitive to cleavage by DNase I - hyper DNase sensitive sites as are nucleosome free
- Different forms of chromatin
- Heterochromatin
- Highly condensed throughout cell cycle
- Highly repetitive 'junk' DNA
- Transcriptionally silent genes
- Enriched in methylcytosine
- Histones underacetylated
- Euchromatin
- DNA decondensed during interphase
- Most genes
- Transcriptionally active genes
- Sensitive to DNAse I digestion
- Facultative heterochromatin
- Switches depending on what is needed
- Heterochromatin
- Position effect variation (PEV)
- Moving genes from heterochromatin -> euchromatin is associated with changes in gene expression - e.g. moving trans genes into heterochromatin; gene won't be expressed (see dolly da sheep!)
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