The Effect of Acetylation and Deacetylation in Post-translational Regulation in Bacteria

Introduction

The processes of transcription and translation are extremely complicated and require a diverse range of enzymatic proteins and cellular machinery to create the desired result, protein. It seems that the simple conversion of DNA to mRNA in transcription and the transformation of mRNA to amino acids is straightforward and continuous. However, the complicated mechanisms involved in creating proteins are intricately regulated at many steps throughout the process.

Transcription begins with the recruitment of RNA polymerase by sigma factors, which recognize the promoters of specific genes to be transcribed. Sigma factors present a very coordinated form of regulation before transcription has even begun. Sigma factors recognize consensus sequences of DNA (common sequences amongst promoters) and therefore can initiate the transcription of multiple proteins. Thus, transcription is carefully regulated by the presence or absence of pertinent sigma factors, which is controlled by sensory mechanisms within the cell that determine stress levels and deficiencies of certain nutrients. The accumulation of a certain sigma factor can cause the transcription of a specific DNA sequence whose gene products are necessary in the cell at that particular time. After sigma binding, the DNA is unwound, and RNA polymerase binds tightly to the DNA. The RNA polymerase then moves along the sequence of DNA, creating mRNA. Transcription is terminated after the stop codon is reached. Even here, the presence of GC rich sequences regulates transcriptional speed and can temporarily halt DNA transcription to allow for the ribosome to catch up in translation. These halts in transcription, either via binding to the protein Rho or the formation of a GC-rich loop, can cause termination if the termination signals are met with RNA polymerase.

Before the RNA sequence can be bound to the ribosome and translated, the ribosome itself must come together. This is initiated with the transcription of rRNA genes that are processed by RNases and configured into a secondary structure. Simulaneously, the ribosomal subunits come together with the rRNA forming the ribosome. With the necessity of transcribing rRNA genes and the presence of the ribosomal subunits, regulation can control whether the cell can and wants to perform translation. Protein elongation occurs when mRNA at the ribosome is met with tRNAs carrying the appropriate amino acid that is coded by the mRNA. Even tRNAs require correct pairing with amino acids before reaching the ribosome; this process is performed by aminoacyl-tRNA transferases. This enzyme could also be modified and hindered, thus regulating translation. The completion of successful protein synthesis is not complete without precise folding of the protein. The correct folding of proteins is crucial to their functioning within the cell. Many proteins are modified by removing the N-formyl group from the N-terminus, by adenylylation, by phosphorylation, or by acetylation, thus regulating their function by modification of the protein itself.

Regulation is occurring at frequent steps in this process of creating a functional protein. This regulation is of vital importance in most cells because of the colossal energy cost of transcription and translation to cells. The formation and functioning of a ribosome alone can consume 40% of a bacterial cell’s energy, and therefore, the unnecessary production of proteins is extremely wasteful to a living cell. This limited energy must be conserved to carry out the numerous functions of the cell, and gene products must only be made when needed. Many stresses induce the need for certain gene products and suppress the need for others. For example, during starvation, many cells activate proteins that break down sugars for sustenance while others may activate ribosomal proteins that will transcribe necessary gene products. Other stresses, such as heat shock, intense pressure, and osmotic stress, may induce the formation or release of stability proteins to help the cell retain itself in extreme conditions. Stresses such as these can be sudden, and an immediate response may be necessary for the survival of the cell. The quickest method of regulation is post-translationally, or the modification of the proteins themselves. It is known that slight changes to the proteins can easily result in the fully inhibited functioning of the molecule. Therefore, as mentioned earlier, the simple addition of an acetyl group (acetylation) can inhibit the functioning of a protein or enzyme, thus controlling its ability to perform within the cell.

Here, the post-translational effect of acetylation and deacetylation on proteins in bacterial cells is investigated, both in regulating proteins involved in cellular processes such as metabolism and in proteins involved in translation itself. In Salmonella enterica, an aerobic, gram-negative bacterium, acetylation of Acetyl-CoA Synthetase (Acs) inhibits its funtion, which transforms Acetate to Acetyl-CoA. A similar mechanism in the gram-positive bacterium Bacillus subtilis is used to regulate Acs by way of an operon. Lastly, Escherichia coli, the gram-negative bacterium commonly found in mammalial intestines, will be investigated as to its effect on ribosomal modulation via acetylation.

Introduce the overall topic of your paper. What microorganisms are of interest? Habitat? Applications for medicine and/or environment? [edit] Section 1

Include some current research in each topic, with at least one figure showing data. [edit] Section 2

Include some current research in each topic, with at least one figure showing data. [edit] Section 3

Include some current research in each topic, with at least one figure showing data. [edit] Conclusion

References

Slonczewski, J. L., J. W. Foster, 2009, Microbiology: An Evolving Science: New York, W. W. Norton & Company, Inc. p. 257-300.