An investigation was carried out to identify different sections of mammalian DNA as either promoters or enhancers of gene Y transcription. Wild-type mammalian cells functioned normally, while mutant cells lacked the ability to produce functional cohesion protein. Based on the data in the table below, which conclusion is valid? $$\begin{array} { | c | c | c | }
\hline \text { Cells } & \text { Regulatory sequence } & \text { Expression of gene } \boldsymbol { Y } \
\hline { \text { Wild-type } } & \mathrm { A } & + + + \
& \mathrm { B } & + + + \
\hline { \text { Mutant } } & \mathrm { A } & + + + \
& \mathrm { B } & 0 \
\hline
\end{array}$$

Question

An investigation was carried out to identify different sections of mammalian DNA as either promoters or enhancers of gene Y transcription. Wild-type mammalian cells functioned normally, while mutant cells lacked the ability to produce functional cohesion protein. Based on the data in the table below, which conclusion is valid? $$\begin{array} { | c | c | c | } 
\hline \text { Cells } & \text { Regulatory sequence } & \text { Expression of gene } \boldsymbol { Y } \
\hline { \text { Wild-type } } & \mathrm { A } & + + + \
& \mathrm { B } & + + + \
\hline { \text { Mutant } } & \mathrm { A } & + + + \
& \mathrm { B } & 0 \
\hline
\end{array}$$

Quizplus · Accepted Answer

The fact that gene Y is expressed in both wild-type and mutant cells when regulatory sequence A is present, but not expressed in mutant cells when only regulatory sequence B is present, suggests that A must be a promoter (necessary for basic gene expression) and B an enhancer (boosts expression but is not essential, and its function can be affected by the lack of cohesion protein in mutant cells).

An Investigation Was Carried Out to Identify Different Sections of Mammalian