3.Discovery of the Operon Cryptic(神秘的、隐藏的mutant Table 7.1 Effect of Cryptic Mutant (lacY-) on Accumulation of Galactoside Accumulation galactoside permease Genotype Inducer of Galactoside☆ Z+Y+ Z+Y+ Z+Y-(cryptic) Z+Y-(cryptic) + B-galactosidase synthesis is induced by lactose At least one more protein is involved in lactose usage
-galactosidase synthesis is induced by lactose At least one more protein is involved in lactose usage Cryptic (神秘的、隐藏的) mutant galactoside permease + _ 3. Discovery of the Operon
Constitutive mutants(组成型突变) How work? P+O+ 2+ r+ A+ lac products in absence of lactose lac products Merodiploid Mutants lac operon wt lac operon (局部二倍体) plasmid Constitutive mutants E.coli P+O+ y+ A+ Merodiploid Wild-type P+ 7+ y+ A+ Constitutive Mutant How to work?Constitutive or inducible?
Constitutive mutants (组成型突变) Merodiploid (局部二倍体) How work? wt lac operon plasmid Constitutive mutants E. coli How to work? Constitutive or inducible？ ConstitutiveMutant Wild-type Merodiploid
Mutant P+ 0+ 7+ lac products in absence of lactose Wild-type lac products / P+o+ Y+ A+ →No lac products in absence of lactose No lac products in the absence of lactose Merodiploid with one wild-type gene and one: (a)Mutant repressor gene(/) Results Conclusion V+ Dominanf No lac products in Inducible absence of lactose Wt produce some substance to keep the Lac genes Both lac operons repressible; Repressor turned off unless they are they are induced. mutation is recessive Y+ A No lac products in absence of lactose No repressor The constitutive mutant had a defected Lacl for repressor,so the mutant is Lac
No lac products in the absence of lactose Mutant Wild-type + Dominant Inducible Wt produce some substance to keep the Lac genes turned off unless they are they are induced. The constitutive mutant had a defected LacI for repressor, so the mutant is LacI-
Some mutations in the operator should abolish its interaction with the repressor, These would also be constitutive mutations (Laco). How can they be distinguished from constitutive mutations in the repressor gene? P+Oc >lac products in absence of lactose lac products
✓Some mutations in the operator should abolish its interaction with the repressor, These would also be constitutive mutations (LacO- ). ✓ How can they be distinguished from constitutive mutations in the repressor gene?
P+OC Z+ y+ Mutant D →lac products in V absence of lactose 十lac products P+O+ 2+ r+ A￥ Wt >No lac products in absence of lactose lac products in the absence oflactose (a)Mutant repressor gene(/) Results Conclusion 1+ P+O+ >No lac products in absence of lactose Inducible Both lac operons Acceptors or doors repressible; Repressor mutation is recessive P+0+ Z+ Y+ A+ No lac products in absence of lactose No repressor Transmitters or cis-dominant(顺式显性)：only with Signal to keep the doors closed respect to gene on the DNA
lac products in the absence of lactose Mutant Wt + Transmitters or Signal to keep the doors closed Acceptors or doors constitutive Acceptors or doors Inducible cis-dominant(顺式显性):only with respect to gene on the DNA