Lec 11 - Alternative Sigma Factors Flashcards

1
Q

Generally, how can the expression and activities of sfs be regulated?

A
  • mRNA secondary structure
  • anti sfs
  • proteolysis
  • anti anti sf
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2
Q

How many sf does E. coli have? List them all.

A

7

  • sf70 - housekeeping
  • sfS - general stress factor
  • sfH - heat shock
  • sfF - flagella synthesis
  • sfI - iron transport
  • sfN - nitrogen metabolism
  • sfE - extracytoplasmic stress
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3
Q

What promoters does sf70 recognise?

A

-35 and -10

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4
Q

How many anti-sf70s exist to sequester sf70 in stationary phase?

A

2 (don’t know which)

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5
Q

At 30C, how is sfH degraded as to not stimulate transcription of heat shock genes?

A

Chaperone proteins, eg DnaK, bind to sfH that has managed to be translated and directs it to protease to be degraded

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6
Q

At 42C why does DnaK and other chaperones not bind to sfH?

A

Preoccupied with binding to other unfolded native proteins in attempt to refold them. Allows sfH to be translated, bind to RNAP (holoenzyme) and initiate transcription of heat shock genes

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7
Q

What promoter elements does sfS recognise?

A

-35 and -10, with slight base sequence differences to sf70. Also binds to same site on RNAP but at lower affinity

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8
Q

When is sfI synthesised?

A

under low Fe conditions (detected by lack of Fur binding to Fe) and when ferric citrate is present (taken up by FecA)

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9
Q

Describe the fec operon

A

Pfur. PfecI. fecIR. Pfur. PfecA. fecABCDE

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10
Q

How is Fe citrate transported into the cytoplasm?

crosses 2 barriers, OM and IM

A

via FecA complex interacting with the TonB complex that provides energy needed for this uptake
from periplasm -> cytoplasm, ABC type transporter, encoded for by fecBCDE?, is used

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11
Q

Why is sfN not classed as part of the sf70 family?

A

Does not spontaneously form an open complex to initiate transcription

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12
Q

What are the promoter sites for sfN?

A

-24 and -12

Also binding sites @ upstream enhancer region

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13
Q

What are the 2 things sfN is dependent upon to initiate transcription? (whilst describing them also try to describe the process)

A
  • NAP, IHF to bend the DNA in order for the enhancer site (with attached activator tfs) to come into contact with the sfN bound to RNAP
  • AAA+ transcription factors that are bound to enhancers. Upon stimulation via a N source, ATP hydrolysis of the tfs occurs and allows the conformational change of sfN to form an open complex w/ RNAP. transcription can then occur and sfN is lost
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