Reference no: EM1389232

You are studying genes and DNAsequences involved in the regulation of the grandoperon.When your lab's strain of e. coli are in the presence of the sugar "grandiose," transcription of two enzymes grandAand grandB increases. You have generated a series of deletion mutants (strains a-e), all of which affect transcription from this operon. You are able to measure the production of the two enzymes because they can also use chemical X as a substrate, turning chemical X pink in the presence of grandA, and blue in the presence of grandB.   Presence of both enzymes will thus appear as purple. (Chemical X itself has no color.)

                                                                                Color of colony when:

Mutation                                               grandiose absent                 grandiose present

None (WT)                                            white                                      purple

   a-                                                         white                                      pink

   b-                                                         white                                      blue

   c-                                                          purple                                     purple

   d-                                                         white                                      white

   e-                                                          purple                                     purple

You create some partial diploids with F' plasmids carrying wild type versions of genes and find the following results in the presence of chemical X. Note that genotypes vary and may include multiple genotypes:

Genotype of                                                                                         Color of colony when:

Chromosome:                      Genotype of F':                 grandiose absent                 grandiose present

a⁺b⁺c⁺d⁺e⁺                             a⁺b⁺c⁺d^-e^-                              white                                      purple

a⁺b^-c^-d⁺e⁺                              a^-b⁺c⁺d⁺e^-                                             blue                                        purple

a⁺b⁺c^-d⁺e^-                              a^-b⁺c^-d⁺e⁺                                             pink                                        purple

a⁺b⁺c⁺d^-e⁺                             a^-b⁺c^-d⁺e⁺                                             pink                                        pink

Using these data, answer the following questions:

1. Is the grand operon inducible or repressible? why? __________________________
2. Indicate which sequence (a, b, c, d, or e) encodes each of the following:

 

Promoter:                            

Operator:                             

Structural gene for grandA enzyme:                              

Structural gene for grandB enzyme                               

Regulatory gene:                               

1. Does the regulatory gene encode a positive or negative regulator of the grand operon? Describe how this system works.