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of foreign genes. In general the expression of foreign genes is carried out in specialised

cloning vectors (Fig. 6.34). However it is possible to use cell-free transcription and

translation systems that direct the synthesis of proteins without the need grow and

maintain cells.In vitrotranslation is carried out with the appropriate amino acids,

ribosomes, tRNA molecules and isolated mRNA fractions. Wheat germ extracts or rabbit

reticulocyte lysates are usually the systems of choice forin vitrotranslation. The resulting

Table 6.3A number of recombinant DNA-derived human

therapeutic reagents

Therapeutic area Recombinant product

Drugs Erythropoietin

Insulin

Growth hormone

Coagulation factors (e.g. factor VIII)

Plasminogen activator

Vaccines Hepatitis B

Cytokines/growth factors GM-CSF

G-CSF

Interleukins

Interferons

Notes:GM-CSF, granulocyte–macrophage colony-stimulating factor; G-CSF,

granulocyte colony-stimulating factor.

Promoter RBS Coding sequence

R T

–35 –10

Start Stop

Prokaryotic expression vector

ori Antibiotic resistance gene

Fig. 6.34Components of a typical prokaryotic expression vector. To produce a transcript (coding sequence) and

translate it, a number of sequences in the vector are required. These include the promoter and

ribosome-binding site (RBS). The activity of the promoter may be modulated by a regulatory gene (R), which

acts in a way similar to that of the regulatory gene in thelacoperon. T indicates a transcription terminator.

235 6.7 Expression of foreign genes