Insulin cloned gene

Insulin receptor gene cloned and mapped to chromosome 19p 13.2-13.3 5... 

Since each of these disorders is caused by the lack of an enzyme, scientists are trying to design a way to replace the lost activity. Oral medication will not work because enzymes are proteins. They would simply be digested, fike any other dietary protein. Enzyme replacement therapy is one approach that is being studied. This would involve periodic injections of the enzyme into the bloodstream, a treatment just fike the injection of insulin by diabetics. Enzyme replacement therapy would require a large supply of the enzyme. Eollowing the model of insulin, the gene for the enzyme could be cloned into bacteria. The bacteria would then produce the protein, which would be purified for use by humans. 

Bacteria are often used as the factories to produce a protein from a cloned gene. This has led to the production of human proteins such as insulin and erythropoietin. 

The first primary P. structure to be determined was that of insulin in 1953. By the end of 1980, over 700 complete primary P. structures had been reported, using the chemical methods of protein analysis described above. Although these methods are still used, in particular for smaller polypeptides and partial sequences, primary P. sequences are now mostly determined from the structure of the cloned gene encoding the P. in question (see Recombinant DNA technology. Nucleic acid sequencing). In 1995, the... 

Human insulin was the first animal protein to be made in bacteria in a sequence identical to the human pancreatic peptide. Expression of separate insulin A and B chains were achieved in Echerichia coli K-12 using genes for the insulin A and B chains synthesized and cloned in frame with the... 

Once a gene is cloned it is necessary to convert the information contained in it into a functional protein. There are a number of steps in gene expression (i) transcription of DNA into mRNA (ii) translation of the mRNA into a protein sequence and (iii) in some instances, post-translational modification of the protein. In discussing these steps in more detail, expression of a cloned insulin gene will be used as an example. 

Fig. 24.5 Insertion of a cloned insulin gene into a vector carrying a bacterial promoter. The arrow indicates the direction of transcription. If we suppose the bacterial promoter is derived from the lactose operon then transcription will be initiated only in the presence of lactose.

Using directed mutation of the cloned receptor gene, Lys 1018 in the ATP-binding part of the tyrosine kinase domain was replaced by alanine. This caused a loss both of kinase activity and of biologic response to insulin.362 Thus, both the tyrosine kinase activity and autophosphorylation appear essential. If so, aggregation of two or more receptors may increase the extent of autophosphorylation and initiate a response. 

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