expression

Examples of expression in the following topics:

• Mammalian Gene Expression in Bacteria

  • In the broadest sense, mammalian gene expression includes every living cell but the term is more normally used to refer to expression as a laboratory tool.
  • An expression system is therefore often artificial in some manner.
  • Viruses and bacteria are an excellent example of expression systems.
  • The oldest and most widely used expression systems are cell-based.
  • There are many ways to introduce foreign DNA to a cell for expression, and there are many different host cells which may be used for expression.

• Riboswitches

  • Riboswitches are naturally occurring RNA molecules that can regulate gene expression.
  • Riboswitches are specific components of an mRNA molecule that regulates gene expression.
  • An mRNA molecule may contain a riboswitch that directly regulates its own expression.
  • The binding of the aptamer to the target molecule results in a conformational change of the expression platform, thus affecting gene expression.
  • The expression platforms, which control gene expression, can either be turned off or activated depending on the specific function of the small molecule.

• Plasmids as Cloning Vectors

  • Vectors called expression vectors (expression constructs) express the transgene in the target cell, and they generally have a promoter sequence that drives expression of the transgene.
  • However, expression vectors have a two expression patterns: constitutive (consistent expression) or inducible (expression only under certain conditions or chemicals).
  • The above conditions are necessary for expression vectors in eukaryotes, not prokaryotes.
  • Allows for antibody identification of cells expressing the target protein.
  • Protein purification tags: Some expression vectors include proteins or peptide sequences that allows for easier purification of the expressed protein.

• Shuttle Vectors and Expression Vectors

  • An expression vector is generally a plasmid that is used to introduce a specific gene into a target cell.
  • An expression vector, otherwise known as an expression construct, is generally a plasmid that is used to introduce a specific gene into a target cell .
  • Once the expression vector is inside the cell, the protein that is encoded by the gene is produced by the cellular-transcription and translation machinery ribosomal complexes.
  • The goal of a well-designed expression vector is the production of large amounts of stable messenger RNA, and in extension, proteins.
  • In general, DNA vectors that are used in many molecular-biology gene-cloning experiments need not result in the expression of a protein.

• Gene Inversion

  • There is also a change in orientation of the DNA that will affect gene expression or the structure of the gene product.
  • Many bacterial species can utilize inversion to change the expression of certain genes for the benefit of the bacterium during infection .
  • The inversion event can be simple by involving the toggle in expression of one gene, like E. coli pilin expression; or more complicated by involving multiple genes in the expression of multiple types of flagellin by S. typhimurium.
  • Fimbrial adhesion by the type I fimbriae in E. coli undergoes site specific inversion to regulate the expression of fimA, the major subunit of the pili, depending on the stage of infection.
  • The FimE recombinase has the capability to only invert the element and turn expression from on to off, while FimB can mediate the inversion in both directions.

• Regulation of Sigma Factor Translation

  • Sigma factors are proteins that regulate gene expression that are controlled at various levels, including at the translational level.
  • Sigma factor expression is often associated with environmental changes that cause changes in gene expression .
  • The regulation of expression of sigma factors occurs at transcriptional, translational, and post-translational levels as dictated by the cellular environment and the presence or absence of numerous cofactors.
  • Using RpoS proteins as the focus, the RpoS expression and transcription is regulated at the translational level.
  • Small noncoding RNAs are able to sense environmental changes and stresses resulting in increased expression of RpoS protein.

• Vectors for Genomic Cloning and Sequencing

  • The purpose of a vector which transfers genetic information to another cell is typically to isolate, multiply, or express the insert in the target cell.
  • Vectors called expression vectors (expression constructs) are specifically for the expression of the transgene in the target cell, and generally have a promoter sequence that drives expression of the transgene.
  • Simpler vectors called transcription vectors are only capable of being transcribed but not translated: they can be replicated in a target cell but not expressed, unlike expression vectors.
  • These plasmid transcription vectors characteristically lack crucial sequences that code for polyadenylation sequences and translation termination sequences in translated mRNAs, making protein expression from transcription vectors impossible.

• Tracking Cells with Light

  • This can be achieved by using tools to monitor gene expression to track when proteins are made and where they go in the cell.
  • It is important to use a reporter gene that is not natively expressed in the cell or organism under study, since the expression of the reporter is being used as a marker for successful uptake of the gene of interest.
  • In cells where the gene is expressed, and the tagged proteins are produced, GFP or luciferase are produced at the same time.
  • GFP as biomarker is also useful in monitoring gene expression and protein localisation in bacterial cells.
  • Reporter gene used as an indication of the regulatory sequence expression in the cell.

• Repression of Anabolic Pathways

  • Transcriptional regulation is the change in gene expression levels by altering transcription rates.
  • Activators enhance the interaction between RNA polymerase and a particular promoter, encouraging the expression of the gene.
  • Regulatory protein is a term used in genetics to describe a protein involved in regulating gene expression.
  • An inducible system is off unless there is the presence of some molecule (called an inducer) that allows for gene expression.
  • A repressible system is on except in the presence of some molecule (called a corepressor) that suppresses gene expression.

• Tests That Differentiate Between T Cells and B cells

  • They are divided into two types based on the pathogen recognition receptors they express on their surface.
  • T-lymphocytes express CD3, CD4, CD8, or CD25 markers.
  • B-lymphocytes express CD19 marker.
  • The expression of different markers allows the separation/differentiation of T and B cells.