Transcriptional Regulation in Prokaryotes

Transcriptional Regulation in Prokaryotes Why might a prokaryote need to regulate gene expression? Metabolism based from external food sources

Operons in Bacteria Operons: Clusters of genes that are under the control of the same promoter. The clusters of genes often control the same metabolic pathways. Why would operons be advantageous?

Operons in Bacteria Operons: Clusters of genes that are under the control of the same promoter. The clusters of genes often control the same metabolic pathways. Why would operons be advantageous? To facilitate coordination of gene expression Bacteria are reliant on what ever food source is available

Operons in Bacteria Operons produce a polycistronic mRNA product The same mRNA contains 3 different proteins

The lac Operon

The lac Operon Lac Operon is regulated by levels of glucose or lactose Glucose is the preferred metabolite Lactose will be used if glucose levels are low B-Galactosidase (B-gal)

The lac Operon Lac Operon is regulated by levels of glucose or lactose Glucose is the preferred metabolite Lactose will be used if glucose levels are low Would glucose positively or negatively regulate the lac operon? Would lactose positively or negatively regulate the lac operon?

The lac Operon Lac Operon is regulated by levels of glucose or lactose Glucose is the preferred metabolite Lactose will be used if glucose levels are low Would glucose positively or negatively regulate the lac operon? Presence of glucose: Negative regulation Lac operon off Would lactose positively or negatively regulate the lac operon? Presence of lactose: Positive regulation Lac operon on

The lac Operon 15

The lac Operon 16

The lac Operon 17

The lac Operon 18

The Lac Operon: Regulation of a Repressor Figure 18-6 The Lac Operon: Regulation of a Repressor Lactose Absent Lactose Present allolactose useable form of lactose 19

Lac Operon: Regulation of the activator CAP II. cAMP positively regulates the CAP activator High glucose=low cAMP Since glucose is present, transcription of lac genes are not needed. No CAP activator recruitment Low glucose=high cAMP Since glucose is low, lactose can be utilized. The CAP activator and cAMP interact which allows the CAP activator sequence to bind to the promoter region. The CAP protein can then recruit RNA poly CAP Activator recruits RNA poly CAP Activator