What is gene expression? A DNA instruction manual

The Takeaway: Gene expression is the way that the information encoded on a gene gets turned into a function. Gene expression is important because it can control when and where RNA molecules and proteins are made, and how much of them are produced. Gene expression can be halted using CRISPR gene editing technology, but it is distinctly different from DNA replication.

Gene expression is the biological process in which the information on a gene is turned into a function. Gene expression can produce proteins or non-coding RNA that affect a phenotype, including transfer RNA and small nuclear RNA. First formulated in the 1950s, gene expression is a process used by all known life forms to generate the molecular machinery that makes life possible, and it involves several key mechanisms, including transcription, mRNA processing, non-coding RNA maturation, translation and translocation, folding, and RNA and protein transport. Let’s look more closely at this important function and get a gene expression definition.

What is gene expression?

The concept of gene expression was mapped out by Francis Crick in 1958. Crick, famous as one of the founders of the structure of DNA, first presented the idea in a symposium then expanded on it in 1970 in an article in Nature, where he described his take on the “central dogma of molecular biology” and how information can or cannot be transferred from a protein to another protein or a nucleic acid. The idea of gene expression was further explained in the discoveries of reverse transcription and RNA replication.

Why is gene expression important?

Gene expression is used by all forms of life to guide how molecular life functions. Gene expression explains how the genotype produces a phenotype, which is the observable traits of an organism. 

What are the key parts of gene expression?

The key parts of gene expression, in rough order of appearance, include: 

• Transcription: The production of an RNA copy from a DNA strand; this is performed by RNA polymerases that add one ribonucleotide at a time to an RNA strand
• Translation: The process where proteins are made using templates created from RNA molecules, with the resultant protein being an amino acid sequence
• mRNA processing: Transcription of protein-coding genes creates messenger RNA (mRNA) that translates into a protein
• Non-coding RNA maturation: Non-coding RNA (ncRNA) are transcribed in different ways to go through additional processing
• RNA export: Most RNA eventually wind up moving from the nucleus to a cytoplasm, and are then transported through nuclear pores to the cytosol; this process uses specific proteins to move the RNA along
• Folding: In the folding process, the unstructured polypeptide folds into a functional coiled three-dimensional structure
• Translocation: The process by which proteins emerge and are directed to an eukaryote or prokaryote
• Protein transport: Some proteins leave the cell using an export pathway

What is gene expression regulation?

A gene’s functional products can't just show up whenever they want—there needs to be some sort of structure, and that is where regulation comes in. Regulation of gene expression refers to the amount and timing of the gene’s functional product. This regulation means that a cell produces only the genes it needs, and only when it needs them, which in turn means that the cell can react to changing environments, changing needs, and even damage.

How is gene expression measured?

Measuring the level at which any one gene is expressed in a cell is important in many pursuits, including bacterial resistance, cancer susceptibility, and viral infection identification. Measuring methods include:

• mRNA quantification: Use of northern blotting or reverse transcription quantitative PCR (RT-qPCR) to gain mRNA molecule size and sequence information
• mRNA/protein correlation: Correlation of a protein and an mRNA
• Protein quantification: Use of western blotting to gauge the size and identify of a protein
• Localization: As opposed to quantification, localization detects mRNA using a complementary mRNA strand and a protein, which results in the identification of its location

Gene expression and CRISPR-Cas9

While gene regulation has typically taken place using observation, CRISPR-Cas9 gene editing is shaking things up by permitting the precise handling of gene expression. IDT offers solutions across all gene expression needs. CRISPR can help researchers understand gene regulation and also alter gene expression and cellular state for a variety of uses.