Regulation of gene expression In bacteriophage lamda RASHIKA RAJASUNDAR
Regulation of gene expression
In bacteriophage lamdaRASHIKA RAJASUNDAR
Lysis or LysogenyLysis: Infection by phage produces many progeny
and breaks open (lyses) the host bacteriumLysogeny: After infection, the phage DNA
integrates into the host genome and resides there passivelyNo progenyNo lysis of the hostCan subsequently lyse
Bacteriophage lambda can do either.
Growth and induction of the Lambda lysogen
Genes responsible for phage expressionN gene – anti terminatorCro gene – lytic switch ONC I gene – lysogenic switch ONC II gene – activation of C I geneC III gene – protects C II geneQ gene – anti terminatorint gene – integrase enzyme
The genetic map of the lambda phage
Recombination Control region Replication LysisVirus head&tail
originoR Pint oL PL PRM PR PRE PR‘
tR3 tL1 tR1 tR2 t6S
attint
xisred
gam
cIII N cI cro cII O P Q S R A…J
promoteroperatorterminator
Late control
cos
Immediate early transcription.
6S RNA
oR Pint oL PL PRM PR PRE PR‘
tR3 tL1 tR1 tR2 t6S
attint
xisred
gam
cIII N cI cro cII O P Q S R A…J
N Cro
Anti-termination by N protein leads to early gene expression.
Pint PL PRM PR PRE PR‘tR3
tL1 tR1 tR2 t6S
attint
xisred
gam
cIII N cI cro cII O P Q S R A…J
N N N
N protein Cro6S RNA
CIII
Recombination proteins
CII
Replication proteins
Q protein
Cro turns off cI, Q protein action leads to late gene expression.
oR Pint oL PL PRM PR PRE PR‘
tR3 tL1 tR1 tR2 t6S
attint
xisred
gam
cIII N cI cro cII O P Q S R A…J
Cro Cro Q
Lytic functionsReplication proteinsViral head & tail proteins
Lysogeny cascade
oR Pint oL PL PRM PR PRE PR‘
tR3 tL1 tR1 tR2 t6S
attint
xisred
gam
cIII N cI cro cII O P Q S R A…J
CIII CII
CI Repressor
PRE = promoter for repressionestablishmentInt
tint
CII
In simple words
Gene expressed first takes up the role.......
Role of Lambda repressor and cro
Summary Both lysis and lysogeny:
synthesize N, Croantitermination by N : synthesize cIII, cII, Q
Lysis:Low [Cro] : binds OR3, shuts off PRM (cI)High [Cro] : shuts off PR and PL
antitermination by Q + activation of PR’ by Cro
Lysogeny:cII stimulate expression from PRE (cI repressor)
and PINT (integrase)cIII stabilizes cIIcI repressor shuts off PR, PL, PR’ (no lytic
functions), stimulates PRM