Chapter 10: transcriptional regulation Fig. 10-1

Regulation of Gene Transcription DNA-binding proteins RNA polymerase binding to the transcription initiation site (e.g., promoter) Regulatory protein(s) binding to other sites (e.g., operator) Regulatory protein binding can positively or negatively regulate transcription

Positive/negative regulation: binding of activator or repressor proteins Fig. 10-2

Regulation of Gene Transcription DNA-binding proteins RNA polymerase binding to the transcription initiation site (e.g., promoter) Regulatory protein(s) binding to other sites (e.g., operator) Regulatory protein binding can positively or negatively regulate transcription Protein affinity for DNA or for other proteins can be influenced by allosteric conformation

Effector binding mediates allosteric change Effector promotes activator binding Effector prevents repressor binding Fig. 10-3

In mammalian newborns, lactose is the principal sugar source for Fig. 10-5 In mammalian newborns, lactose is the principal sugar source for intestinal flora

Lactose utilization by E. coli -linked disaccharide peculiar to milk lac genes encode a glycosidase and proteins that promote cellular import of lactose Genes are transcribed only in the presence of lactose (inducible) and the absence of glucose (catabolite repression) Genes are organized into a co-transcribed cluster (operon; encodes a polycistronic mRNA)

(simplified schematic) lac operon in E. coli (simplified schematic) Fig. 10-4

lac operon in E. coli (dynamic schematic) Fig. 10-6

Fig. 10-8

Fig. 10-9

Fig. 10-10

Effects of mutations within consensus sequences of E. coli promoters Fig. 10-11

Effects of lac operator mutations Fig. 10-12

E. coli lac is also regulated by catabolite repression Regulates preferential utilization of glucose Mediated by cAMP (glucose-responsive) cAMP is effector of catabolite activator protein (CAP) cAMP-CAP binds to lac promoter, enhancing binding of RNA polymerase

Fig. 10-13

Fig. 10-13

Activated CAP binding induces a distortion of its DNA binding site “presents” P region to RNA polymerase Fig. 10-15

Molecular organization of the lac promoter region Fig. 10-16

Cumulative regulatory control of lac transcription Fig. 10-17

Cumulative regulatory control of lac transcription Fig. 10-17

“Negative control” (repression) “Positive control” (activation) Fig. 10-18

Typical 5’ end sequences found in eukaryote genes (promoter and nearby elements) RNA polymerase binding site Fig. 10-22

β-globin promoter region and effects of mutation Consensus sequences predict important regions which experiments can often confirm Fig. 10-23

Eukaryote polymerase binding and transcription initiation are determined by cooperative interactions of diverse proteins with diverse DNA sequences Enhancer-binding factors can be tissue-specific Near DNA sequences: promoter-proximal elements Distance-independent DNA sequences: enhancers/silencers Fig. 10-24

Drosophila dpp gene region contains many tissue-specific enhancers Visceral mesoderm enhancer (VM) Lateral mesoderm enhancer (LE) Imaginal disk enhancer (ID) Most tissue/cell-specific gene expression in eukaryotes is controlled by enhancers Fig. 10-27

Chromosome rearrangements that create new physical relationships among genes can result in gain-of-function mutation The In(3R)Tab mutation brings into close proximity: sr enhancer sequences (drive thorax expression) Abd-B gene (product drives expression of abdominal pigmentation) +/+ Tab/+ Fig. 10-28

Chromatin structure influences gene expression Euchromatin: rich in active genes Heterochromatin: Constitutive heterochromatin (e.g., centromere regions) few active genes Facultative heterochromatin: euchromatin in some cells, heterochromatic in others rich in genes; genes are transcriptionally silent Epigenetic inheritance: inheritance of genes with same DNA sequence, but different levels of expression

Mammalian X-chromosome heterochromatization dosage compensation inactivation of one X in female cells (heterochromatic X is “Barr body”) selection of X occurs in early embryo (then is fixed for clonal populations) mammalian females mosaically express their X-linked genes Fig. 10-30

Imprinting: recently discovered in mammals DNA methylation usually results in reduced levels of gene expression Differential methylation of genes and transmission of that methylation can result in imprinting phenomena Fig. 10-32

Prader-Willi syndrome can arise “de novo” through a combination of mutation and imprinting Fig. 10-31

Position-effect variegation (PEV): relocation of euchromatic genes to the vicinity of heterochromatin can result in mosaic inactivation Clonal-determined heterochromatin spreading Fig. 10-34

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Fig. 10-