Cambridge A-Level Biology – Principles of Genetic Technology
Principles of Genetic Technology
Objective
Explain why a promoter may have to be transferred into an organism together with the desired gene.
Key Concepts
Gene expression – the process by which information from a gene is used to synthesize a functional product, usually a protein.
Promoter – a DNA sequence located upstream of a coding region that binds RNA polymerase and transcription factors to initiate transcription.
Vector – a DNA molecule (plasmid, virus, or artificial chromosome) used to deliver foreign genetic material into a host cell.
Host organism – the recipient cell or organism that receives the recombinant DNA.
Why Transfer a Promoter?
When a gene is moved from one organism to another, the regulatory environment of the host may differ dramatically from that of the donor. The native promoter of the donor gene often does not function efficiently in the new host for several reasons:
Species‑specific transcription factors – Promoters contain binding sites for transcription factors that may be absent or differ in the host.
Chromatin structure – In eukaryotes, promoter accessibility is influenced by histone modifications that are species‑specific.
Regulatory signals – The donor promoter may respond to environmental cues not present in the host, leading to little or no transcription.
Expression level requirements – Desired applications (e.g., production of insulin, vaccine antigens) often need high, constitutive, or inducible expression that the native promoter cannot provide.
Expression only under specific conditions (e.g., presence of IPTG)
T7 promoter with lac repressor, tetracycline‑controlled promoter
Tissue‑specific promoter
Expression limited to a particular cell type
Albumin promoter (liver), keratin promoter (skin)
Illustrative Example
Consider the production of human insulin in E. coli:
The human insulin gene is isolated from pancreatic DNA.
The native human promoter does not function in bacteria because it requires eukaryotic transcription factors.
A bacterial promoter such as the lac promoter is placed upstream of the insulin coding sequence in a plasmid vector.
The recombinant plasmid is introduced into E. coli, where the lac promoter drives high‑level transcription of the insulin gene, allowing large‑scale protein production.
Key Points to Remember
Promoters are essential for initiating transcription; without a functional promoter, the transferred gene remains silent.
Choosing the appropriate promoter depends on the host organism, desired expression level, and whether expression should be constitutive, inducible, or tissue‑specific.
In many cloning vectors, a multiple cloning site (MCS) is positioned downstream of a pre‑installed promoter to simplify gene insertion.
Regulatory compliance often requires that the promoter used does not contain antibiotic‑resistance genes or other undesirable elements.
Suggested diagram: Schematic of a recombinant DNA construct showing a promoter, coding sequence, terminator, and selectable marker within a plasmid vector.
Summary
Transferring a promoter together with the desired gene ensures that the gene can be transcribed efficiently in the host organism. The promoter must be compatible with the host’s transcriptional machinery and suited to the experimental or commercial objectives. Selecting the right promoter is a critical step in the design of any genetic engineering project.