Micro Exam 3 - Transcriptional and Translational Regulation

What are transcriptional regulation methods?

alternative sigma factors, DNA-binding proteins, riboswitches

Sigma A is the ______________ sigma.

housekeeping

Sigma B is the _________________ sigma.

stress response

Sigma D is the _______________ sigma.

motility

Sigma H is the _________________ sigma.

starvation

What do most alternative sigma factors have?

specific anti-sigmas

What do specific anti-sigmas do?

inhibit by protein interaction

What can disconnect anti-sigma and activate alternative sigma?

environmental stimuli

What is FlgM?

a classic anti-sigma that binds to sigma D and inhibits motility because DNAP cannot bind to site

What DNA binding proteins regulate transcription?

Lac operon, 2 component system, quorum sensing

What is LacY?

lactose permease that transports lactose into the cell

What is LacZ?

β-galactosidase that cleaves lactose into glucose and galactose

How is the Lac operon activated?

cAMP-CAP binds to the promoter

Describe the cAMP-CAP relationship.

CAP binds to DNA and stabilizes RNAP at promoter ONLY when cAMP is present, cAMP is synthesized by adenylate cyclase which is inhibited by glucose

What is LacI?

repressor protein that binds to the lac operator and severely bends the DNA, preventing access of RNAP to lac promoter

In absence of lactose...

expression of lac operon wastes resources - so it is regulated so that the operon is expressed only when lactose is present

Describe Lac operon de-repression.

when lactose (inducer) is present, it prevents DNA binding of repressor and exposes weak promoter - requires CAP activation

What is diauxic growth?

sequential use of different carbon sources leading to different growth rates (glucose consumed first, then lactose)

What are the two components to regulate transcription by DNA-binding proteins in a system?

histidine protein kinase (HPK) and response regulator (RR)

What does HPK do?

receive signal

What does RR do?

control gene expression

Describe the process of the two-component system used to regulate transcription.

1 - in response to the signal, HPK autophosphorylates on a histine residue, 2 - HPK transfers phosphate to an aspartate on the RR, 3 - phosphorylation activates DNA binding and RNAP recruitment

Two-component systems used for transcriptional regulation are...

modular

What is quorum sensing?

sensing the number of bacteria in a population required to trigger changes in gene expression

Cells indirectly sense...

their own population density and respond by changes in gene expression

Cells directly sense...

an extracellular signaling molecule

What extracellular signaling molecule do cells directly sense?

autoinducers

Each species of bacteria make...

a structurally unique autoinducer and can only sense their own

Autoinducers are an example of...

intra-species cell communication

What is LuxI?

autoinducer synthase that acts as a DNA binding transcriptional activator and needs high concentrations of autoinducer

Describe the process of direct sensing in quorum sensing.

1 - autoinducer constantly synthesized at fixed rate, 2 - autoinducer passively diffuses out of cell and into environment, 3 - as autoinducer accumulates in environment, diffusion causes it to equilibrate in cell, LuxR binds to autoinducer and then to DNA which activates transcription and gene expression

The autoinducer accumulates _____________________ cell density.

in proportion with

What are riboswitches?

an RNA sequence patter in the 5' leader of mRNA that folds to regulate transcription

Describe how riboswitches work.

Riboflavin binds directly to the transcript and the transcript folds to form a transcriptional terminator at the front of the operon

What are translational regulation methods?

small regulatory sRNA, CsrA

Describe the process of how sRNA regulates translation.

1 - an RNA chaperon Hfq binds to sRNAs, 2 - Hfq then delivers sRNAs to target transcripts, 3 - sRNA interacts with specific transcript and blocks SD to inhibit translation

What is CsrA?

an RNA binding protein

Describe how CsrA regulates translation.

binds stem loops to block SD of some transcripts, inhibits translocation by blocking ribosomal access