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SIGNAL TRANSDUCTION
• BACTERIA SENSE CHANGE IN ENVIRONMENT AND RESPOND TO IT
• TWO COMPONENT SIGNAL TRANSDUCTION SYSTEMPHOSPHO-RELAY SYSTEM
SENSOR KINASE DETECTS CHANGE IN ENVIRONMENT (e.g.,
FOOD) TRANSMITS SIGNAL TO RESPONSE
REGULATOR BY PHOSPHORYLATING IT
KINASES TRANSFER PHOSPHORYL GROUPS (KINASES CAN PHOSPHORYLATE
THEMSELVES)
RESPONSE REGULATOR PHOSPHORYLATED PROTEIN CONTROLS TRANSCRIPTION / OR PROCESS
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GLOBAL REGULATORY SYSTEMS
REGULONS - MANY GENES AND OPERONS CONTROLLED SIMULTANEOUSLY
ALLOW CELLS TO RESPOND TO CHANGING ENVIRONMENTS BY TURNING ON SETS OF GENES
NOT NEEDED FOR DAILY LIVING
EXAMPLES: FOOD - CHEMOTAXIS HEAT SHOCK DAMAGE TO CHROMOSOME FOOD DEPRIVATION
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CATABOLITE REPRESSION REGULON - OPERONS INVOLVED IN SUGAR CATABOLISM REQUIRE cAMP-CAP FORTRANSCRIPTION INITIATION. GLUCOSE ALSO PRESENT IN THE MEDIUM MEANS THAT THOSE OPERONS CANNOT BE TURNED ON.
LACTOSE, ARABINOSE, GALACTOSE, RIBOSE OPERONS ARE PART OF CATABOLITE REPRESSION REGULON
LACTOSE -> GALACTOSE AND GLUCOSEL-ARABINOSE -> D-XYLULOSE-5-PO4
GALACTOSE -> GLUCOSE-1-PO4
RIBOSE -> D-XYLULOSE-5-PO4
GLUCOSE INHIBITS cAMP SYNTHESIS, PREVENTS ANY OF THOSE OPERONS TO BE TURNED ON. WHY? GLUCOSE ISMORE EFFICIENT CARBON SOURCE
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SOS REGULON –
1. SET OF ~50 GENES WHICH CODE FOR PRODUCTS WHICHREPAIR DNA DAMAGE AND HELP SURVIVAL AFTER DNA DAMAGE
COMMON SOS REPRESSOR, COMMON SOS OPERATORSBEFORE THE SOS GENES
ENZYMES TO REMOVE DAMAGED NUCLEOTIDES ANDAND FILL IN NORMAL NUCLEOTIDES - NO MUTATIONS
ENZYMES POLYMERIZE PAST DAMAGED NUCLEOTIDESBUT INSERT RANDOM NUCLEOTIDES - MANY MUTATIONS
ENZYMES TO RECOMBINE BROKEN CHROMOSOMES GENERATES ONE INTACT CHROMOSOME
PROTEIN TO DELAY CELL DIVISION – PROVIDES TIME TOCOMPLETE DNA REPAIR
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2. WHAT IS THE SOS SIGNAL? SINGLE STRANDED DNA FRAGMENTS (OR SINGLE STRANDED REGIONS OF DNA) CREATED BY DAMAGE – RADIATION, CHEMICALS, ANTIBIOTICS
3. WHAT RECOGNIZES SIGNAL?
RecA PROTEIN IS ACTIVATED BY BINDING SINGLE STRANDED DNA THAT IS, DAMAGED DNA
4. WHAT TURNS ON THE SOS GENES?
ACTIVATED RecA PROTEIN STIMULATES SOS REPRESSOR TO CLEAVE ITSELF
INACTIVE SOS REPRESSOR CAN NO LONGER BIND SOS OPERATOR OR REPRESS THOSE ~50 GENES
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Regulation of the SOS response regulon in E. coli. (A) About 50 genes around the E. coli chromosome are normally repressed by the binding of a LexA dimer (barbell structure) to their operators. Some SOS genes are expressed at low levels, as indicated by single arrows. (B) After DNA damage, the single-stranded DNA (ssDNA) that accumulates in the cell binds to RecA (circled A), forming a RecA nucleoprotein filament, which binds to LexA, causing LexA to cleave itself. The cleaved repressor can no longer bind to the operators of the genes, and the genes are induced as indicated by two arrows. The approximate positions of some of the genes of the SOS regulon are shown.
SOS RESPONSE6
RECOMBINATION
SOSREPRESSOR
CELL DIVISIONINHIBITOR
UVREPAIR
TRANS-LESION
DNAPOLYMERASE
RecADNA DAMAGE
SENSOR
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8
14
15
11
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STAGE 0VEGETATIVE CELL
STAGE IAXIAL
FILAMENTATIONOF DNA
STAGE IIASYMMETRIC
SEPTATION
STAGE IIIENGULFMENT
STAGE IVCORTEX
[PEPTIDOGLYCAN]SYNTHESIS
STAGE VCOAT
SYNTHESIS
STAGE VIMATURATION
[FULLY RESISTANT]
STAGE VIIMOTHER CELL
LYSIS
2. ENDOSPORE FORMATION (IN RESPONSE TO NUTRIENT DEPLETION)13
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SENSORKINASE - P
SENSORKINASE
SpoOF
SpoOF - P
SpoOB
SpoOB - P
SpoOA
SpoOA - P
RESPONSEREGULATOR =
MASTER CONTROLLER
PHOSPHO-RELAY
PROTEINS
PHOSPHORY-LATES ITSELFDUE TO GTP
CONCEN-TRATION
DROP
SIGNAL TRANSDUCTION TO INITIATE SPORULATION
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RESPONSE REGULATOR SpoOA-P
ACTS WITH RNA Pol- s A
BINDS OA SITES NEAR s A PROMOTERS
CONTROLS REGULON OF 121 GENES
30 INDIVIDUAL24 OPERONS
ACTIVATES GENES FOR:AXIAL FILAMENT ORGANIZINGASYMMETRIC SEPTATIONSIGMA FACTORS
FORESPORE EARLY & LATEMOTHER CELL EARLY & LATE
INHIBITS GENES FOR:DNA REPLICATION; MOTILITY;
CHEMOTAXIS
5’ TTTGTCGAAAAA 3’
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PROTEINS SYNTHESIZED IN SPECIALIZED COMPARTMENTS& IN CORRECT TEMPORAL ORDER
FORESPORE – EARLY ENGULFMENT FACTOR, GERMINATION FACTOR
MOTHER CELL – EARLY ENGULFMENT FACTOR, CORTEX PEPTIDOGLYCANSYNTHESIS ENZYMES
FORESPORE – LATEDNA REPAIR ENZYMES, DNA BINDING PROTEINS TOREDUCE WATER CONTENT, PROTECT DNA
MOTHER CELL – LATESPORE COAT PROTEINS, SPORE SURFACE SUGARSYNTHESIS (FOR ATTACHMENT)
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COUNTERCLOCKWISESWIM FORWARD
CLOCKWISETUMBLES
RANDOMLY(DIRECTIONCHANGES)
RECEPTORS
BIASED RANDOM WALK(TUMBLE LESS OFTENWHEN APPROACHING
ATTRACTANT)
CHEMOTAXIS RECEPTORS E. COLI
YELLOW PROTEINS ATCELL POLE
TAKE HOME: SIGNAL TRANSDUCTION DEPENDS ON SENSORS AND
RESPONSE REGLATORS (USUALLY REGULATE TRANSCRIPTION)
REGULONSDNA REPAIR PROCESSESSPORULATION AS A DEVELOPMENTAL PROCESS
PROTEINS ARE MADE IN RIGHT COMPARTMENT AT THE TIME THEY ARE NEEDED
CHEMOTAXIS