Lecture 2 - Regulation of Bacterial Gene Expression Flashcards
When is toxin produced by bacteria?
During stationary phase
What is a bacterial gene locus?
A linear segment of DNA that has multiple genes
Define transcription unit.
A sequence of DNA bases that is transcribed to give a single, discrete complimentary RNA (can be multiple genes in bacteria known as an operon).
Which bacterial RNA polymerase subunit is necessary for the core polymerase to recognize promoter regions? Is it involved in transcription?
Sigma. It is released after the core polymerase binds (not involved in transcription).
Are sigma subunits specific to promoters?
Yes, there are many sigma subunits that recognize specific promoter sequences.
What factor is “factor dependent” transcription termination dependent upon?
Rho factor.
How does Rho factor work?
It binds directly to RNA polymerase, causing termination.
What is a positive regulator?
A protein that binds DNA upstream of the promoter region and helps load RNA polymerase on to the promoter.
How does a negative regulator work?
They bind directly to the promoter to sterically hinder RNA polymerase from binding.
What is a feature of the factor independent termination sequence?
It is a region of dyad symmetry (inverted repeat)
How is tcdR involved in regulation of C. dificile toxin gene expression?
tcdR encodes a sigma factor that is specific for the toxin gene promoters.
How is tcdR gene expression regulated?
By cod Y. It is a general repressor that binds the promoter region of tcdR, inhibiting transcription of the sigma subunit that can result in toxin production.
How is Cod Y regulated?
By the amino acid isoleucine. Cod Y binds isoleucine when it is in abundance, which activates Cod Y, inhibiting transcription of tcdR. During nutritional limitation isoleucine is not available, and Cod Y is inactive. This allows for transcription of tcdR, which leads to sigma subunits, which leads to toxin production.
What is tcdC and how does it work? Why is it needed?
It is a negative regulator (an anti-sigma factor) that binds to sigma subunits, preventing them from being active and making toxin. It is needed because small amounts of sigma must be present to begin transcription of the toxin genes immediately after Cod Y is deactivated.
What do rifamycins do?
Block RNA synthesis elongation.
