BIOCHEMISTRY - L. Stryer - 1984

VOLUME 3

Part IV INFORMATION

CHAPTER 28. THE REGULATION OF GENE EXPRESSION IN THE PHENOTYPE

PROBLEMS AND QUESTIONS

1. What will be the outcome of the following Mutations?

a) Deletion of the lac Operon regulatory Gene.

b) Deletion of the trp operon regulatory gene.

c) Deletion of the ara operon regulatory gene.

d) Deletion of the cI gene of phage

e) Deletion of the N gene of phage .

2. Super-repressed lac operon mutants (i^s) behave as uninducible mutants. The i^s gene is dominant to the i⁺ gene in partial diploids. What might be the Molecular Mechanism of this mutation?

3. An E. coli mutant has been isolated that synthesizes large amounts of β-galactosidase regardless of whether an inducer is present in the medium. Partial diploids generated from this mutant and F'i⁺o⁺z^- also synthesize high levels of β-galactosidase independently of the inducer. What kind of mutation could lead to this result?

4. A wild-type culture yielded a mutant unable to grow on galactose, lactose, arabinose, and several other carbon sources. The intracellular concentration of cyclic AMP in the mutant is normal. What type of mutation could account for this phenotype?

5. An E. coli Cell carrying prophage is immune to lytic infection by this phage. Why?

6. METABOLISM/31.html">Transcription of cI can be initiated from the p_RE promoter, which is responsible for establishing Lysogeny, or the p_RM promoter, which maintains it. Transcripts from p_RM begin with the 5'-terminal AUG codon of the repressor, whereas the p_RE transcript has a sequence preceding this initiation codon that is complementary to the 3'-terminal sequence of 16S rRNA. Initiation at the p_RE site requires phage-encoded Proteins that are not expressed in the lysogenic state.

a) Which transcript will be translated with greater efficiency?

b) What is the possible physiological significance of this difference?