HC 5: Sigma factors, 2 component systems, chemotaxis

Genetic competence

Foreign DNA can be taken up through pores. RecA promotes the invasion and exchange of DNA strands, AddAB works with breaks and creates single stranded DNA overhangs.

Sigma factor

Protein needed for transcription, transcription initiation factor that enables binding of DNA polymerase to promotors. Forms holoenzyme with RNA polymerase Recognizes two regions of promotor:
-Pribnow box
- -35 region
When transcription starts, sigma factor is released. Various sigma factors with various functions

Spore formation

Asymmetric division leads to forespore and the rest of the cell being divided within the cell. Forespore is taken up into the mothercell through engulfment. DNA outside of the spore is broken down and a exosporangium gets created. Cell wall is lost and a spore is formed. 

Sporulation regulation

Cascade of activated sigma factors results in sporulation. Sigma A activates sigma F. There is membrane level cell division resulting in two parts with sigma F. Then the bigger compartments sigma F turns into sigma E. Engulfment leads to sigma G in the future spore. Rest of the cell contains sigma K.

Anti-sigma factor

Unfolded proteins which link to a PDZ domain will trigger the release of sigma E. RseA is the anti-sigma factor which  controls the activation of sigma E

·       Sensor kinase

·       Often in membrane. Detects environmental signal and autophosphorylates.

Response regulator

DNA binding protein that regulates transcription and is activated by phosphorylation by the sensor kinase. Can be dephosphorylated by specific phosphatases.

Two component system

A stimulus-response coupling mechanism. Typically consist of sensor kinase and a response regulator. These systems often form complex phosphorylation cascades (phosphorelay) that allow multiple inputs.

Initiating sporulation

Sensor kinase phosphorylates itself through input of other phosphorylases the chain continues (SpoOF and SpoOB) > the response regulator (SpoOA) is activated (master controller) and sporulation starts

Chemotaxis

Ability of organisms to sense chemical gradients and modify its motility in response. Bacteria swim towards chemoattractants and away from chemorepellentsusing their flagella.

·       Tumbling an running. Tumbling is movement in multiple random rotations with flagella distributed along the cell and running is straight movement in random reorientation with flagella bundeled. Movements keep happening until a better concentration is found.

TipA

·       TlpA membrane-bound methyl-accepting chemotaxis receptor accumulates at curved membranes. Shape mismatch between protein and membrane drives protein to curved membranes where there is reduced tension. Important for bacteria don’t contain organelles or cytoskeletons to transport proteins to cell