Gene expression

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Gene expression , also expression or expression for short , denotes in a broad sense how the genetic information - of a gene (section of DNA ) - is expressed and appears, i.e. how the genotype of an organism or a cell is expressed as a phenotype . In a narrower sense, gene expression is understood to mean the biosynthesis of proteins (see protein biosynthesis ) on the basis of the genetic information together with all the preceding processes necessary for this, beginning with the transcription as the synthesis of RNA .

The different gene expression is, for example, one cause of the slightly different phenotype in (genetically identical) identical twins; in genetically different individuals, the differences in the phenotype are based not only on the modification but also primarily on differences in the genome . The temporal and spatial differences in gene expression are referred to as spatiotemporal gene expression .


The transcription is the synthesis of RNA by RNA polymerases to the DNA template. The RNA strands that code for proteins are called messenger RNA (mRNA). In eukaryotes , these arise in the cell nucleus from the primary nuclear transcript through RNA processing . In addition to possible RNA interference and possible RNA editing, this includes splicing and adding a cap structure and a poly (A) tail before the core export. The following translation is the synthesis of a protein by ribosomes in the cytoplasm using the mRNA present. The base sequence of the mRNA is translated with the help of transfer RNA (tRNA) into the coded amino acid sequence of the generated polypeptide chain, which gains the native three-dimensional protein structure through protein folding . As a rule, proteins are modified post-translationally .

General, as well as cell- and development-specific transcription factors that bind DNA, regulate transcription. The prerequisite for this is the accessibility of the Loci . Since the DNA is not naked, but packed, wrapped and folded, a gene can be inaccessible due to the dense chromatin structure ( heterochromatin ) or more or less withdrawn from transcription due to changes in chromatin proteins. In this way, transcriptional regulation of gene expression is also possible epigenetically .

The post-transcriptional factors include the stability of the mRNA, its localization and its degradation, the translational factors include initiation and elongation on the ribosomes and the availability of (loaded) tRNA, while the stability of the proteins formed, their interactions and any processes that are fed back via them Then influence gene expression post-translationally.


In general, gene expression can be regulated at different levels. The above-mentioned principles can interact with one another - especially in the case of eukaryotes - and thus form even more complex regulatory mechanisms in the interaction of genetics and epigenetics .

Some genes are not subject to any such regulation and are expressed consistently and consistently regardless of cell type , cell stage and growth conditions. These genes are constitutively expressed, including many housekeeping genes . The constitutive enzymes they encode maintain the basic functions of a cell.


A large number of molecular biological experiments make it possible to examine the expression, i.e. the relative or absolute amount of RNA in a cell, a tissue or a developmental stage. These include Northern blot analysis, quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), the RNase protection assay and in situ hybridization . These methods are used to detect one or a few transcripts. In-situ hybridization with radioactive , digoxigenin-labeled or fluorescent antisense RNA samples enables the spatial transcript distribution to be examined. If one intends to determine a large spectrum, or all RNAs in a sample, one speaks of transcriptomics . This includes DNA chip technology (synonymous with DNA microarray ), with which a large number of previously identified transcripts can be quantified in parallel. With the serial analysis of gene expression (SAGE, from English Serial Analysis of Gene Expression ) there is an effective method for the identification of short cDNA fragments, so-called tags , which were obtained from mRNA molecules by means of the enzyme reverse transcriptase . The latest alternative is the "total transcriptome shotgun sequencing", also known as RNA-Seq , which places high demands on bioinformatic analysis.

Specific antibodies , which are used in various immunassays , are required for the detection of known proteins . Western blot analysis allows statements to be made about the relative amount and size of the proteins to be examined. The enzyme-linked immunosorbent assay (ELISA) and the radioimmunoassay are suitable for quantitative investigations . Protein microarrays , also known as biochips , have been developed for high throughput . They allow the parallel analysis of a large number of proteins in a small amount of biological sample material. The spatial distribution of proteins is examined with immunohistochemical and immunocytochemical investigations. Analogous to the transcriptome, there is also an attempt to depict the proteome of cells. However, the challenges to the rapidly developing proteomics are much greater, also because the number of different proteins in a cell, which exceeds the number of genes many times over. The most important detection devices are mass spectrometers , which are becoming more and more precise, sensitive and faster.


  • Nelson C. Lau, David P. Bartel: Censorship in the cell . Spectrum of Science, October 2003, pp. 52-59, ISSN  0170-2971
  • Lubert Stryer: Biochemistry , 4th edition, spectrum, Heidelberg- Berlin - Oxford 1996, ISBN 3-86025-346-8 , ( V. replication and expression of genes , p. 825 ff)
  • Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 5th edition. Freeman, New York 2002, ISBN 0-7167-4684-0 , available online from the NCBI Bookshelf.

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