The light-producing genes of V. fischeri are organized in an operon that is under positive control by an activator protein called LuxR. Would you expect the genes of this operon to be transcribed when LuxR is bound or not bound to a DNA regulatory sequence? Explain.

Verified step by step guidance

1. Understand the role of LuxR: LuxR is an activator protein, which means it facilitates the transcription of genes by helping RNA polymerase initiate transcription when it is bound to a DNA regulatory sequence.
2. Identify the control mechanism: Since the operon is under positive control by LuxR, the presence of LuxR bound to the DNA enhances the transcription of the genes within the operon.
3. Consider the effect of LuxR binding: When LuxR is bound to the DNA regulatory sequence, it activates the transcription of the light-producing genes in the operon of V. fischeri.
4. Analyze the scenario when LuxR is not bound: If LuxR is not bound to the DNA regulatory sequence, the operon will not be actively transcribed because the positive control by LuxR is absent, leading to low or no transcription of the light-producing genes.
5. Conclude the transcription status: Based on the role of LuxR as an activator in positive control, you would expect the genes of this operon to be transcribed when LuxR is bound to a DNA regulatory sequence.

Key Concepts

Operon Structure

An operon is a cluster of genes under the control of a single promoter, allowing for coordinated expression. In prokaryotes, operons enable the regulation of genes that encode proteins with related functions, facilitating efficient resource use. The organization of genes in an operon allows for simultaneous transcription and translation, which is crucial for rapid responses to environmental changes.

Positive Control in Gene Regulation

Positive control refers to the mechanism by which an activator protein enhances the transcription of a gene or operon. In the case of V. fischeri, the LuxR protein binds to a specific DNA sequence, promoting the recruitment of RNA polymerase to the promoter region. This interaction increases the likelihood of transcription occurring, thereby facilitating the expression of light-producing genes when conditions are favorable.

Transcription Factors

Transcription factors are proteins that bind to specific DNA sequences to regulate gene expression. They can act as activators or repressors, influencing the transcription of target genes. In the context of the LuxR protein, its binding to the DNA regulatory sequence is essential for initiating transcription of the operon, highlighting the critical role of transcription factors in gene regulation.