Fig. 10-1

Chapter 10: transcriptional regulation

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

Fig. 10-2

Positive/negative regulation:binding of activator or repressor proteins

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

Fig. 10-3

Effector binding mediates allosteric change

Effector promotes activator binding

Effector prevents repressor binding

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)

Fig. 10-4

lac operon in E. coli(simplified schematic)

Fig. 10-6

lac operon in E. coli

(dynamic schematic)

Fig. 10-8

Fig. 10-9

Fig. 10-10

Fig. 10-11

Effects of mutations withinconsensus sequences of E. coli promoters

Fig. 10-12

Effects of lac operator mutations

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

Fig. 10-15

Activated CAP bindinginduces a distortion

of its DNA binding site

“presents” P regionto RNA polymerase

Fig. 10-16

Molecular organization of the lac promoter region

Fig. 10-17

Cumulative regulatorycontrol of lac transcription

Fig. 10-17

Cumulative regulatorycontrol of lac transcription

Fig. 10-18

“Negative control”(repression)

“Positive control”(activation)

Fig. 10-22

Typical 5’ end sequences found in eukaryote genes

(promoter and nearby elements)

RNA polymerasebinding site

Fig. 10-23

β-globin promoter region and effects of mutation

Consensus sequences predict important regionswhich experiments can often confirm

Fig. 10-24

Eukaryote polymerase binding and transcription initiationare determined by cooperative interactions ofdiverse proteins with diverse DNA sequences

Near DNA sequences: promoter-proximal elements

Distance-independent DNA sequences: enhancers/silencers

Enhancer-binding factors can be tissue-specific

Fig. 10-27

Drosophila dpp gene region contains many tissue-specific enhancers

Lateral mesoderm enhancer (LE) Imaginal disk enhancer (ID)

Visceral mesoderm enhancer (VM)

Most tissue/cell-specific gene expression in eukaryotesis controlled by enhancers

Fig. 10-28

Chromosome rearrangements thatcreate new physical relationshipsamong genes can result in gain-of-function mutation

The In(3R)Tab mutationbrings into close proximity:

• sr enhancer sequences (drive thorax expression)

• Abd-B gene (product drives expression of abdominal pigmentation)

+/+ Tab/+

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 othersrich in genes; genes are transcriptionally silent

Epigenetic inheritance: inheritance of genes with same DNA sequence, but different levels of expression

Fig. 10-30

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

Imprinting: recently discovered in mammals

DNA methylation usuallyresults in reduced levelsof gene expression

Differential methylationof genes and transmissionof that methylation canresult in imprintingphenomena

Fig. 10-32

Fig. 10-31

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

Fig. 10-34

Position-effect variegation (PEV): relocation of euchromatic genesto the vicinity of heterochromatin can result in mosaic inactivation

Clonal-determined heterochromatin spreading

Fig. 10-

Fig. 10-