L4 Transcription Initiation and Termination

Question 1

Component 1

Answer 1

Has two domains:

1. input domain
2. transmitter domain
   - kinase activity
   - phosphatase activity

Question 2

Transmitter domain

Answer 2

• kinase, with input signal

- phosphatase, without input signal

Question 3

Component 2

Answer 3

1. Receiver domain
2. output domain - activated to to regulate gene expression, generally a DNA binding domain, activated protein may be positive/negative regulator

Question 4

Kinase activity

Answer 4

adds P to histidine (autophosphorylation), with input signal&raquo_space; activated to interact with receiver domain of component 2 (P transferred to Aspartate of receiver domain of component 2)

Question 5

Porins

Answer 5

Protein form pores in membrane

influences permeability of solutes into cell

Question 6

Osmolarity

Answer 6

High osmolarity - kinase

Low osmolarity - phosphatase

Question 7

Nitrogen

Answer 7

• regulate PII activity
• regulation of N assimilation
• NtrB = component 1
• NtrC = component 2
• regulates glnA gene expression

low N = kinase, activates glnA exp.
high N = phosphatase, basal glnA exp

Question 8

glnA

Answer 8

structural gene for Glutamine synthetase, links together glutamate and ammonia to make glutamine

Question 9

Nitrogen - sigmas

Answer 9

sigma70 used when N levels are high at the P1 promoter
sigma54 used when N levels are low at the P2 promoter

sigma70 can activate initiate transcription without activator
sigma54 cannot proceed to open complex without an activator - NtrC is the activator (P transferred from NtrB to NtrC)

Question 10

NtrC

Answer 10

• ATPase activity: catalyses open complex formation by interaction with rna pol holoenzyme, this often requires DNA bending

Question 11

Intrinsic - Rho-independent termination

Answer 11

• complementation in GC rich region of mRNA
• stem and loop structures
• string of U’s
• weaker A-U base to assist with transcript release

Question 12

Rho factor dependent

Answer 12

• protein
• hexamer binds to mRNA
• uses ATP
• helicase unwinds DNA-RNA duplex
• binds to rut site
  Rho attaches to mRNA once the rut sequence has been transcribed

Question 13

Rut site

Answer 13

• high C, low G sequence in mRNA
• precedes termination point
• Rho attaches to mRNA once the rut sequence has been transcribed

Question 14

“Polarity”

Answer 14

Premature termination of translation can cause premature termination of transcription

Question 15

Anti-termination

Answer 15

• control mechanism
• binds to specific sequences separate from terminator sequences
  e. g. N gene of lambda

Question 16

Phosphatase Activity

Answer 16

removes P group from receiver domain of component 2, output domain of component 2 is inactivated

Question 17

Rho Action

Answer 17

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