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

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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