1 SIGNAL TRANSDUCTION BACTERIA SENSE CHANGE IN ENVIRONMENT AND RESPOND TO IT TWO COMPONENT SIGNAL TRANSDUCTION SYSTEM PHOSPHO-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

2 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

3 CATABOLITE REPRESSION REGULON - OPERONS INVOLVED IN SUGAR CATABOLISM REQUIRE cAMP-CAP FOR TRANSCRIPTION 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 GLUCOSE L-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 IS MORE EFFICIENT CARBON SOURCE

4 SOS REGULON – SET OF ~50 GENES WHICH CODE FOR PRODUCTS WHICH REPAIR DNA DAMAGE AND HELP SURVIVAL AFTER DNA DAMAGE COMMON SOS REPRESSOR, COMMON SOS OPERATORS BEFORE THE SOS GENES ENZYMES TO REMOVE DAMAGED NUCLEOTIDES AND AND FILL IN NORMAL NUCLEOTIDES - NO MUTATIONS ENZYMES POLYMERIZE PAST DAMAGED NUCLEOTIDES BUT INSERT RANDOM NUCLEOTIDES - MANY MUTATIONS ENZYMES TO RECOMBINE BROKEN CHROMOSOMES GENERATES ONE INTACT CHROMOSOME PROTEIN TO DELAY CELL DIVISION – PROVIDES TIME TO COMPLETE DNA REPAIR

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6 SOS RESPONSE SOS REPRESSOR CELL DIVISION INHIBITOR RECOMBINATION UV REPAIR TRANS- LESION DNA POLYMERASE RecA DNA DAMAGE SENSOR 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.

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2. ENDOSPORE FORMATION (IN RESPONSE TO NUTRIENT DEPLETION) 13 2. ENDOSPORE FORMATION (IN RESPONSE TO NUTRIENT DEPLETION) STAGE 0 VEGETATIVE CELL STAGE I AXIAL FILAMENTATION OF DNA STAGE II ASYMMETRIC SEPTATION STAGE III ENGULFMENT STAGE IV CORTEX [PEPTIDOGLYCAN] SYNTHESIS STAGE V COAT SYNTHESIS STAGE VI MATURATION [FULLY RESISTANT] STAGE VII MOTHER CELL LYSIS

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SIGNAL TRANSDUCTION TO INITIATE SPORULATION 16 SIGNAL TRANSDUCTION TO INITIATE SPORULATION SENSOR KINASE - P PHOSPHORY- LATES ITSELF DUE TO GTP CONCEN- TRATION DROP SpoOF SENSOR KINASE SpoOB - P SpoOF - P SpoOA SpoOB PHOSPHO- RELAY PROTEINS SpoOA - P RESPONSE REGULATOR = MASTER CONTROLLER

RESPONSE REGULATOR SpoOA-P 17 ACTS WITH RNA Pol- s A BINDS OA SITES NEAR s A PROMOTERS CONTROLS REGULON OF 121 GENES 30 INDIVIDUAL 24 OPERONS ACTIVATES GENES FOR: AXIAL FILAMENT ORGANIZING ASYMMETRIC SEPTATION SIGMA FACTORS FORESPORE EARLY & LATE MOTHER CELL EARLY & LATE INHIBITS GENES FOR: DNA REPLICATION; MOTILITY; CHEMOTAXIS 5’ TTTGTCGAAAAA 3’

18 PROTEINS SYNTHESIZED IN SPECIALIZED COMPARTMENTS & IN CORRECT TEMPORAL ORDER FORESPORE – EARLY ENGULFMENT FACTOR, GERMINATION FACTOR MOTHER CELL – EARLY ENGULFMENT FACTOR, CORTEX PEPTIDOGLYCAN SYNTHESIS ENZYMES FORESPORE – LATE DNA REPAIR ENZYMES, DNA BINDING PROTEINS TO REDUCE WATER CONTENT, PROTECT DNA MOTHER CELL – LATE SPORE COAT PROTEINS, SPORE SURFACE SUGAR SYNTHESIS (FOR ATTACHMENT)

COUNTERCLOCKWISE SWIM FORWARD CLOCKWISE TUMBLES RANDOMLY (DIRECTION RECEPTORS CLOCKWISE TUMBLES RANDOMLY (DIRECTION CHANGES)

BIASED RANDOM WALK (TUMBLE LESS OFTEN WHEN APPROACHING ATTRACTANT)

CHEMOTAXIS RECEPTORS E. COLI YELLOW PROTEINS AT CELL POLE

TAKE HOME: SIGNAL TRANSDUCTION DEPENDS ON SENSORS AND RESPONSE REGLATORS (USUALLY REGULATE TRANSCRIPTION) REGULONS DNA REPAIR PROCESSES SPORULATION AS A DEVELOPMENTAL PROCESS PROTEINS ARE MADE IN RIGHT COMPARTMENT AT THE TIME THEY ARE NEEDED CHEMOTAXIS