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Download Discussion of control of the lac operon and mutational analysis
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Transcript
The lac Operon Laboratory Purpose: Learning to analyze an example of gene expression Example: lac operon Type of control: negative inducible Today’s Laboratory Work on mutational analysis problem of lac operon; page 3-24 Lac Operon: Negative Control and Induction Repressor has two binding sites. Lactose binding site DNA binding site The promoter needs to be in an ideal conformation for RNA polymerase. An overview of regulation of the lac operon Let review a few terms and then look at the lab problem (table) on page 3-24 important terms of DNA control. 3 important terms of DNA control. Constitutive activity Trans acting Cis acting Examples of cis and trans acting elements Cis acting: c O mutation Trans acting I mutation Trans acting: s I mutation Laboratory Exercise Haploid and Heterozygous Diploid Mutants Predict if you expect to obtain: transcription/translation of the lacZ and lacY genes when lactose is absent or present for the E.coli. Try out your ability to reason through the questions. PROTEIN PRODUCT Β-galactosidase No Lactose I+P+O+Z+Y+ I-P+O+Z+Y+ I+P-O+Z+Y+ I+P+OcZ+Y+ I+P+O+Z-Y-/ I-P+O+Z+Y+ I+P+OcZ+Y-/ I+P+O+Z-Y+ I+P+OcZ-Y+/ I-P+O+Z+YISP+O+Z+Y-/ I-P+O+Z-Y+ I+P-OcZ+Y+/ I+P+O+Z-Y- - Lactose + Permease No lactose - Lactose + The next slides are a “key” to the mutations. Experimental tests on the repressor: I+ cells synthesize full levels of the lac enzymes only in the presence of an inducer I- mutations NO DNA BINDING ACTIVITY, TRANSCRIPTION OCCURS EVEN IN ABSENCE OF INDUCER! Is mutation NO LACTOSE BINDING ACTIVITY but has DNA BINDING ACTIVITY. NO TRANSCRIPTION EVEN WITH INDUCER! Experimental mutations to the repressor I s=inducer binding region mutated Inhibits transcription, even with inducer Lactose binding site DNA binding site I - = DNA binding site mutated, prevents binding, allows transcription The End.
