Lac Operon: Positive & Negative Transcriptional Regulation - Essay Sample

Introduction

The lac operon has both positive and negative transcriptional regulation. Negative regulation is easier to understand. The i gene product of the lac operon is a protein called lac repressor, which is a macromolecular repressor binding the lac operator and blocking RNA polymerase from binding and thereby blocking transcription (Jackson, 2017). Negative regulation occurs by the introduction of an inducer that activates the synthesis of the gene products that are involved in catabolism by the removal of a barrier to the transcription.

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Positive Control

The positive control of the lac operon, the lactose promoter, differs from ideal -35 and -10 sequences that do not function efficiently by self-stimulation transcription as RNA polymerase does not bind well. There is a positive activator protein known as CRP or the Cyclic AMP Protein that binds specific sequences adjacent to the promoter assisting RNA polymerase in binding to the promoter (Phillips et al., 2019). For the function to stimulate the RNA polymerase that binds to the lac promoter, the CRP must bind to AMP. It, therefore, undergoes conformational changes, which greatly increase the affinity for some DNA sites, including one in the lac operon adjacent to the RNA polymerase binding site.

Advantages

One of the advantages of the lac operon is the use of E. coli in experimental and industrial purposes. LacZ gene encoded the β- galactose and used as a reporter in the prokaryotic and eukaryotic systems (Phillips et al., 2019). It is one of the reliable reporter systems in tracking and monitoring the products of lacZ genes (Stefanski et al., 2016). However, it also has limitations. Although the system is suitable in the qualitative analysis of gene expression, the product needs to have further experimental procedures such as lysate preparation. Therefore the system is unsuitable for high throughput screening.

References

Jackson, R. C. (2017). The Boolean kinetics of signal transduction. Bioinformatics, 24(18), 2044-2050. https://www.researchgate.net/profile/Robert_Jackson18/publication/320908715_The_Boolean_Kinetics_of_signal_transduction/links/5a01d5ac0f7e9bfd74604d69/The-Boolean-Kinetics-of-signal-transduction.pdf

Phillips, K. N., Widmann, S., Lai, H. Y., Nguyen, J., Ray, J. C. J., Balázsi, G., & Cooper, T. F. (2019). Diversity in lac operon regulation among diverse Escherichia coli isolates depends on the broader genetic background but is not explained by genetic relatedness. mBio, 10(6). https://mbio.asm.org/content/mbio/10/6/e02232-19.full.pdf

Stefanski, K. M., Gardner, G. E., & Seipelt-Thiemann, R. L. (2016). Development of a lac operon concept inventory (LOCI). CBE—Life Sciences Education, 15(2), ar24. https://www.lifescied.org/doi/pdf/10.1187/cbe.15-07-0162