12. Gene Regulation in Prokaryotes

Northern blot analysis is performed on cellular mRNA isolated from E. coli. The probe used in the northern blot analysis hybridizes to a portion of the lacY sequence. Below is an example of the gel from northern blot analysis for a wild-type lac⁺ bacterial strain. In this gel, lane 1 is from bacteria grown in a medium containing only glucose (minimal medium). Lane 2 is from bacteria in a medium containing only lactose. Following the style of this diagram, draw the gel appearance for northern blots of the bacteria listed below. In each case, lane 1 is for mRNA isolated after growth in a glucose-containing (minimal) medium, and lane 2 is for mRNA isolated after growth in a lactose-only medium.

lac⁺ bacteria with the genotype I⁺ P⁺ Oᶜ Z⁺ Y⁺ 

A bacterial inducible operon, similar to the lac operon, contains three genes—R, T, and S—that are involved in coordinated regulation of transcription. One of these genes is an operator region, one is a regulatory protein, and the third produces a structural enzyme. In the table below, '+' indicates that the structural enzyme is synthesized and '−' indicates that it is not produced. Use the information provided to determine which gene is the operator, which produces the regulatory protein, and which produces the enzyme.

Genotype                          Enzyme Synthesis
                             Inducer Present      Inducer Absent
R⁺S⁺T⁺                               +                          –
R⁻S⁺T⁺                                –                          –
R⁺S⁻T⁺                                +                          +
R⁺S⁻T⁺                                +                          +
R⁻S⁺T⁺/R⁺S⁻T⁻                      +                          +
R⁺S⁻T⁺/R⁻S⁺T⁻                      +                          +
R⁺S⁺T⁻/R⁻S⁻T⁺                      +                          –

For the following lac operon partial diploids, determine whether the synthesis of lacZ mRNA is 'constitutive,' 'inducible,' or 'uninducible,' and indicate whether the partial diploid is  or  (able or not able to utilize lactose).