CIII protein protects CII from proteolytic degradation'

1
CIII protein protects CII from proteolytic
degradation. Growth in rich medium activates
host proteases CII is degraded, l enters the
lytic cycle. In poor media, CII is not
degraded. ? more frequently lysogenises starving
cells.
2
CII also activates 2 other promoters
PRE
cI
PI
xis
int
P anti-Q
Int protein functions in integration of phage
genome. P antiQ transcript is an anti-sense RNA
that further blocks lytic gene expression.
3
attP
xis
int
Integrase
attB
4
xis
int
5
Prophage induction results from proteolytic
cleavage of cI repressor Cro protein is then
synthesised.
Cro binds to OR3 and blocks cI transcription.
Lytic gene transcription starts from PR and PL.
6
xis
int
On prophage induction int and xis are expressed
from PL A complex of integrase and excisionase
excise the phage genome.
7
WEAK cI at OR2 facilitates RNA pol binding
8

PR
-35
-10 Cro
TTGACT GATAAT
Start point 5 CATACGTTAAATCTATCACCGCAAGGGATAAATA
TCTAACACCGTGCGTGTTGACTATTTTTACCACTGGCGGTGATAATGGTT
GCATGTA 3 OR3
OR2 OR1 3
GTATGCAATTTAGATAGTGGCGTTCCCTATTTATAGATTGTGGCACGCAC
AACTGATAAAAATGGTGACCGCCACTATTACCAACGTACAT 5
TTAGAT ATAGAT
-10 -35
PRM
5 CTGATGTGCTCAGTATCACCGCCAGTGGTATTTATGTCAACACC
GCCAGAGATAATTTATCACCGCAGATGGTTATCTGTAT 3
OL1 OL2
OL3 3 GACTACACGAGTCATAGTGGCGGTCACCATAA
ATACAGTTGTGGCGGTCTCTCTTAAATAGTGGCGTCTACCAATAGACTAT
5 TCATAG ACAGTT
-10 -35
PL