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GENE - M3 > Phage Lambda > Flashcards

Phage Lambda Flashcards

(52 cards)

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1
Q

CI repressor + function

A

maintains lambda as prophage in lysogenic state by repressing main promoters and activating its own expression

represses genes required for lytic cycle

FOR LYSOGENIC PATHWAY

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2
Q

Cro

A

expressed early in infection and the major player in establishing lytic growth

DNA-binding protein that represses transcription “promoting” lytic cycle

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3
Q

CII

A

major activator protein in deciding the lytic or lysogenic fate of lambda following infection.

DNA-binding protein that activates transcription “promoting” lysogenic cycle

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4
Q

levels of CII are affected by…

A

host proteases

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5
Q

CIII

A

protein protects CII from degradation by proteases

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6
Q

N

A

anti-terminator protein that enables transcription past certain terminators resulting in early gene expression

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7
Q

Q

A

another anti-terminator that enables expression of late lytic genes such as head, tail and lysis genes

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8
Q

Int

A

promotes integration (between attP and attB sites) of the lambda genomes into the host genome for the establishment of lysogeny

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9
Q

virus =

A

infectious agent that must grow or reproduce inside a host cell

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10
Q

bacteriophage =

A

viruses that infect bacterial cells

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11
Q

phage lambda (info)

A

infects E. coli

siphoviridae
dsDNA
long, flexible tail
icosahedral head

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12
Q

3 main points of phage lambda lifecyle

A

DNA injection in E.coli and circularisation
deciding
lytic or lysogenic pathway

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13
Q

lytic pathway

A

many viral chromosomes in bacteria
viral assembly
cell lysis

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14
Q

lysogenic pathway

A

recombination and integration
either prophage induction (cell lysis) or lysogenic growth

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15
Q

DNA injection and circularisation

A

genome = linear in phage head
after injection = circularises

aided by cohesive end sites (cos sites)

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16
Q

lytic cycle: phage assembly and release

A

head and tail proteins synthesises
DNA packaged into heads
tails added
host is lysed, releasing new phage

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17
Q

lysogenic cycle: phage integration and maintenance

A

lambda integrates
prophage is stably maintained
prophage passed to daughter cells

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18
Q

lysogeny - integration of lambda DNA into host chromosome

A

occurs in 2 sites = attP and attB

site-specific recombination requiring enzyme Int (integrase)

lambda linearised in host chromosome

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19
Q

VERY early gene expression events

A

following injection - host RNA pol transcibres 2 promoters

P l = produces N
P r = produces Cro

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20
Q

cro gene

A

encodes cro protein
- major player in establishing lytic growth

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21
Q

Early gene expression events

Study These Flashcards
A

N encodes an anti-terminator protein that enables transcription past 2 terminators resulting in early gene transcription

22
Q

how is the ‘decision’ made?

Study These Flashcards
A

host proteases degrade CII (healthy cells produce high amount) - therefore in actively growing cells CII is degraded

Cro win = lytic cycle

23
Q

What is the deciding protein

24
Q

in the ‘decision’ the main 2 proteins deciding are…

25
Late lytic
CII degraded, Cro predominates Cro represses expression of CI - all early genes then itself and replication genes Q = anti-terminator that enables expression of late lytic genes
26
how does the cell decide to go into lysogenic cycle
starved cells produce less protease CII remains intact and stable - turns on int (integrase) - integrates lambda into host chromosome - CI repressor (activates own expression) binds to OL and OR to repress all other phage genes
27
late lysogenic: maintenance of lysogeny
maintained as a prophage by CI = repressor - keeps phage genome 'silent' in bacterial chromosome until induction
28
late lysogeny: stable prophage
CII - promotes int and CI integration of DNA via int CI maintain prophage
29
2 main proteins in lytic pathway + function
Cro - represses CI Q - anti-terminates lytic genes
30
2 main protein in lysogenic pathway + function
CII - activates CI (repress main promoters) and Int (integrate into chromosome)
31
main protein in lysogeny maintenance
CI
32
what something that makes the lysogenic pathway switch to lytic
UV - inactivates CI Cro is synthesised - lytic cycle
33
switch in lysogeny (whats on whats off)
CI ON and Cro OFF (maintenance)
34
switch in lytic (whats on whats off)
Ci OFF and Cro ON (induction)
35
what are the components of the switch
Operator (1, 2, and 3 - for CI and Cro) and promoter (RM and R)
36
the RNA pol will.... on the switch
will bind to EITHER operator - never both
37
Pr activity by RNA pol
doesnt need a regulatory protein
38
P rm activity by RNA pol
needs CI as an activator
39
Pr is a...
strong promotr - RNA pol has strong affinity - always transcribes Cro
40
P rm is a...
weak promoter - needs CI as an activator promotes transcription by helping RNA pol come to DNA
41
affinities can determine____ relative to _____
order of binding concentration of protein
42
CI in the switch
is dimeric via C-terminal interactions - uses their N-terminal domain to bind DNA Each Or site can bind one Ci dimer along one side of the DNA helix
43
controls of CI in the switch (+ and -)
negative = CI at Or2 turns OFF cro grne by preventing RNA pol from binding to cro promoter (exclusion) positive = CI at Or2 helps RNA pol bind and begin transcription of Ci gene + increases the affinity for P rm by providing protein-protein interactions in addition to the protein-DNA interactions
44
CI protein prefers...
Or1 and Or2 - therefore binding there and blocking RNA pol (will then have to bind to Or3 and transcribed CI)
45
2 factors contributing to CI binding
1. intrinsic affinity (always wants to be on CI) 2. cooperativity
46
why does CI not bind at Or3
dimers 'lean' towards each other. Or3 binding cant be cooperative since CI C-terminal domains unavailable binding at Or2 can stil bind RNA pol since it interacts with N-terminus
47
UV induction =
DNA damage - breaks stable state - can cause prophage to enter lytic cycle
48
explain CI cleavage (in induction)
induction via UV = DNA damage - damage sensed by RecA resulting it becoming a co-protease RecA assists CI cleavage into 2 domains (non-functional) and therefore celars the operator sites of CI
49
results of CI cleavage
activation of Prm (Ci) lost repression of excision genes lost (decreased CI) RNA pol binds to Pr and transcribes cro cro now determines the course of events lose repression of Pint and the Int and Xis proteins are made Xis/Int promote excision of lambda from host
50
cro in the switch
cro dimers can bind to each Or site int eh absence of CI cro binds on once side of the DNA helix cro has a sinlge domain 2 monomers of cro form dimers almost all cro in the cell is dimeric
51
induction - effect of cro
cro binds to each operator site independently cro is ONLY A NEGATIVE REGULATOR binding to Or3 stops any possible Ci expression expression from Pr also enables phage lytic gene expression Ci expression shut down and late lytic genes expression can occur (lytic cycle) - cro later shuts off its own transcription and that of early phage lytic genes
52
2 proteins related to induction/switch (only from lysogenic to lytic)
CI degraded cro Promotes lytic cyle

GENE - M3 (3 decks)

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