The Stringent Response

Question 1

Bacterial metabolism is regulated by

Answer 1

small molecules

• secondary messengers: ppGpp + cyclic di-GMP
• quorum sensing molecules (AHLs)

Question 2

secondary messengers are

Answer 2

molecules produced in response to a stimulus and then detected by something else to mediate a response

Question 3

The stringent response causes a

Answer 3

global decrease in rna synthesis

ppGpp is a normal guanine diphosphate with a phosphate attached on the 3’ end

particularly affects rRNA and tRNA synthesis

by reducing the amount of tRNA and rRNA the cell will reduce the rate of translation which will conserve the a.a. supply

Question 4

ppGpp is an (3)

Answer 4

ALARMONE
alarm signal that signals the need to shut down RNA production
mediates the stringent response
it is an effector that can be phosphorylated to pppGpp

Question 5

how do cells sense a shortage of an amino acid

Answer 5

ribosomes stall on mRNA at codons with uncharged tRNAs as they enter A site (with no a.a. on them due to shortage)
this activates RelA

Question 6

pppGpp is made by

Answer 6

RelA using pppGpp synthase

pppGpp converted back to ppGpp by pppGpp phosphohydrolase

Question 7

RelA is an enzyme on

Answer 7

approx 1 in 200 ribosomes

RelA is activated when an uncharged tRNA enters the A site of the ribosome

Question 8

SpoT can also

Answer 8

make and get rid of pppGpp

SpoT also responds to C, P and Fe starvation and oxidative stress

Question 9

pppGpp binds to

Answer 9

RNA polymerase

stops transcription of rRNA and tRNA, ribosomal proteins, cell wall production and DNA replication

Question 10

pppGpp turns on

Answer 10

stress proteins
amino acid biosythesis pathways
recycling proteolases
stationary phase sigma factors

Question 11

What is particularly sensitive to pppGpp in rRNA and tRNA?

Answer 11

the discriminator region

this is a promotor with a high GC content in the -10 to +1 region

this region melts during transcription initiation and the high GC content makes this difficult

promotors which have a high GC content are more sensitive to pppGpp

Question 12

How does ppGpp work?

Answer 12

makes open complex formation allosterically unfavourable, especially for GC rich discriminators

this is because it binds to RNA pol and affects the ability of the transcription bubble to form

AT rich sequences are less affected

Question 13

AT rich sequences can be

Answer 13

activated by pppGpp

as transcription slows, more rRNA in the cell = more AT rich sequences transcribed = more stringent response proteins

Question 14

RNA pol is a major transducer of

Answer 14

pppGpp signal

Question 15

Outside reading info

Answer 15

secondary effects of ppGpp’s role in regulating expression of other gene products or binding to enzymes other than RNAP. It has been reported that ppGpp affects the activities of DNA primase, lysine decarboxylase, IF2, and guanylate kinase, regulating processes as varied as DNA replication, translation, and
central metabolism. Furthermore, ppGpp is required for virulence in many pathogens

ppGpp’s effects are amplified by DksA, a 17.5 kDa protein that modifies RNAP by binding to the enzyme’s secondary channel