A muscle enzyme called ME1 is produced by transcription and translation of the ME1 gene in several muscles during mouse development, including heart muscle, in a highly regulated manner. Production of ME1 appears to be turned on and turned off at different times during development. To test the possible role of enhancers and silencers in ME1 transcription, a biologist creates a recombinant genetic system that fuses the ME1 promoter, along with DNA that is upstream of the promoter, to the bacterial lacZ (β-galactosidase) gene. The lacZ gene is chosen for the ease and simplicity of assaying production of the encoded enzyme. The diagram shows bars that indicate the extent of six deletions the biologist makes to the ME1 promoter and upstream sequences. The blue deletion labeled D is within the promoter whereas the gray bars span potential enhancer/silencer modules. The table displays the percentage of β-galactosidase activity in each deletion mutant in comparison with the recombinant gene system without any deletions.





Why does deletion D effectively eliminate transcription of lacZ?

Verified step by step guidance

1. Analyze the diagram and table provided. The diagram shows the ME1 gene structure, including the upstream region, promoter, and lacZ gene. The deletions (A-F) are marked as gray bars, with deletion D specifically within the promoter region. The table shows the percentage of lacZ activity for each deletion mutant compared to the control (no deletion). Deletion D results in <1% lacZ activity.
2. Understand the role of the promoter in transcription. The promoter is a DNA sequence that serves as the binding site for RNA polymerase and other transcription factors, initiating transcription of the downstream gene. If the promoter is disrupted, transcription cannot occur effectively.
3. Interpret the data for deletion D. Since deletion D is within the promoter region and results in <1% lacZ activity, this suggests that the deleted region is critical for the binding of RNA polymerase or transcription factors necessary for initiating transcription.
4. Compare deletion D to other deletions. Deletions A, B, and C, which are upstream of the promoter, do not significantly affect lacZ activity, indicating that these regions may not contain essential elements for transcription initiation. Deletion E increases lacZ activity, suggesting it may remove a silencer element, while deletion F reduces activity, possibly removing an enhancer element.
5. Conclude that deletion D effectively eliminates transcription of lacZ because it disrupts the promoter region, which is essential for RNA polymerase binding and transcription initiation. Without a functional promoter, the lacZ gene cannot be transcribed.

Key Concepts

Gene Regulation

Gene regulation refers to the mechanisms that control the expression of genes, determining when and how much of a gene product is produced. This process is crucial for cellular differentiation and response to environmental changes. In the context of the ME1 gene, regulation involves enhancers and silencers that can activate or repress transcription, influencing the production of the ME1 enzyme in muscle tissues.

Promoter Function

The promoter is a specific DNA sequence located upstream of a gene that serves as the binding site for RNA polymerase and transcription factors. It is essential for initiating transcription. Deletion D, located within the promoter region of the ME1 gene, likely disrupts the necessary interactions for transcription initiation, leading to the observed elimination of lacZ expression.

Enhancers and Silencers

Enhancers and silencers are regulatory DNA sequences that can increase or decrease gene transcription, respectively. Enhancers can be located far from the promoter and interact with it through DNA looping, while silencers inhibit transcription. The experiment's design, which includes deletions in potential enhancer/silencer regions, helps to elucidate their roles in regulating ME1 transcription and the resulting lacZ activity.