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Eukaryotic Gene Regulation
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5 mechanisms Chromatin Structure Transcriptional Posttranscriptional
Translational Posttranslational
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Chromatin Structure Which of these is more accessible to the kitten? A
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Unacetylated histones Acetylated histones
Figure 15.7 Nucleosome Histone tails Unacetylated histones Acetylated histones Figure 15.7 A simple model of the effect of histone acetylation 4
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Heterochromatin is like a ball of yarn!
RNA polymerase cannot reach heterochromatin! Euchromatin = the sweet stuff! (DNA accessible to RNA polymerase
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Barr Bodies An X chromosome is packed away as heterochromatin
Why only in females? Evidence of Chromatin structure regulating gene product
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Transcriptional Control
Just like prokaryote, # 1 way to control gene activity Much more complex!
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Major Players Promoter – low level of gene activity
Transcription factors – proteins that regulate Transcription activators – bind to enhancers
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The rest of the Major Players
Enhancers – DNA can be far from promoter! Responsible increased level of gene activity Repressors – much less of a role in eukaryotes silencers
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Enhancer (distal control elements)
Figure 15.8a Enhancer (distal control elements) DNA Upstream Proximal control elements Poly-A signal sequence Transcription start site Exon Intron Exon Intron Exon Promoter Figure 15.8a A eukaryotic gene and its transcript (part 1) Transcription termination region Downstream 11
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Poly-A signal sequence Transcription start site
Figure 15.8b-2 Proximal control elements Poly-A signal sequence Transcription start site Exon Intron Exon Intron Exon DNA Promoter Transcription Poly-A signal Primary RNA transcript (pre-mRNA) Exon Intron Exon Intron Exon 5 Cleaved 3 end of primary transcript Figure 15.8b-2 A eukaryotic gene and its transcript (part 2, step 2) 12
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Poly-A signal sequence Transcription start site
Figure 15.8b-3 Proximal control elements Poly-A signal sequence Transcription start site Exon Intron Exon Intron Exon DNA Promoter Transcription Poly-A signal Primary RNA transcript (pre-mRNA) Exon Intron Exon Intron Exon 5 Cleaved 3 end of primary transcript RNA processing Figure 15.8b-3 A eukaryotic gene and its transcript (part 2, step 3) Intron RNA Coding segment mRNA G P P P AAAAAA 3 Start codon Stop codon 5 Cap 5 UTR 3 UTR Poly-A tail 13
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Distal control element Enhancer TATA box
Figure Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA- bending protein Group of mediator proteins Figure A model for the action of enhancers and transcription activators (step 2) 14
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Distal control element Enhancer TATA box
Figure Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA- bending protein Group of mediator proteins RNA polymerase II Figure A model for the action of enhancers and transcription activators (step 3) RNA polymerase II Transcription initiation complex RNA synthesis 15
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After Transcription RNA processing Splicing
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Translational Control
Longevity of RNA
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Translational Control
RNA induced silencing complex microRNAs bind to mRNA Degrade or inhibit translation
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Post translation Protein is present and active!
Cell can degrade it at different rate (proteosomes) Cyclin proteins
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