Transcriptional control of GS Flashcards
(14 cards)
Transcriptional control of GS is
slower than post translational and allosteric control
PII controls the activity of
NtrB
a sensor histidine kinase in a two component system
The NtrB/C system
when N is low, PII has UMP attached
histidine kinase NtrB recognises this and phosphorylates response regulator NtrC
NtrC-P activates transcription of large numbers of genes encoding N SCAVENGING SYSTEMS
including glnA which makes GS!!
When a cell has high levels of NtrC-P it signals
severe nitrogen deficiency
What does NtrB sense?
Whether PII has UMP attached
histidine kinase NtrB also acts as a
phosphatase
can remove P from NtrC-P
PII controls its activity
When N is low, PII has UMP attached and has no effect on NtrB so it acts as a
kinase
When N is high, PII does not have UMP, and turns NtrB into a
phosphatase
Low N = PII-UMP =
NtrB kinase
High N = PII =
NtrB phosphatase
Summary of PII in NtrB/C
UTase senses the gln:2oxoglut ratio
UTase feeds this into PII
PII feeds into NtrB
NtrB feeds into NtrC
N scavenging genes only on when N is low
What does RR NtrC-P do?
activates N scavenging operons
e.g. the GS operon
Promotor 2 in the operon is a high level inducible promotor that requires NtrC-P and sigma factor 54 to work
How does NtrC-P stimulate transcription? (2)
by sigma 54 activation:
NtrC-P loops (closed complex formation) the DNA so RNA pol + sf54 can bind to the promotor
by helicase activity
melts the DNA to form a transcription bubble
the gln operon contains
the genes for NtrC and B, therefore they induce their own synthesis
