1. The lac Operon Laboratory
Purpose: Learning to analyze an example of gene expression
Example: lac operon
Type of control: negative inducible

2. The Laboratory Worksheet asks: How do mutations affect gene expression of the lac operon?

3. Review: Lac Operon:

4. Mutations and gene expressio of lac operon

5. Oc mutation: a cis acting mutation

6. I- mutation a trans acting mutation

7. Is mutation a trans acting mutation

8. Lab Worksheet: 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.

9. Try out your ability to reason through the questions.

10. - + - + 1 2 3 4 5 6 7 8 9 Β-galactosidase Permease I+P+O+Z+Y+
Lactose
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+Y-
ISP+O+Z+Y-/ I-P+O+Z-Y+
I+P-OcZ+Y+/ I+P+O+Z-Y-
No Lactose 1 - + 2 3 4 5 6 7 8 9

11. The End.

12. Laboratory Exercise

13. Try out your ability to reason through the questions.

14. - + - + PROTEIN PRODUCT Β-galactosidase Permease Lactose No lactose
I+P+O+Z+Y+ - +
I-P+O+Z+Y+
I+P-O+Z+Y+
I+P+OcZ+Y+
I+P+OcZ+Y-/ I+P+O+Z-Y+
I+P+OcZ-Y+/ I-P+O+Z+Y-
ISP+O+Z+Y-/ I-P+O+Z-Y+
I+P-OcZ+Y+/ I+P+O+Z-Y-
No Lactose - +
I+P+O+Z-Y-/ I-P+O+Z+Y+

15. The next slides are a “key” to the mutations.

16. 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!

17. 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