Cloned gene expression transcription

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. 

Figure 2 Comparison of cloning and expression methods. In the conventional strategy (left), dehydrogenase genes obtained by PCR amplification of the original source DNAs are cloned into overexpression plasmids and verified by sequencing. Those with the desired structure are individually transformed into suitable host strains and the proteins are obtained, either as crude extracts or as purified samples. In the proposed streamlined approach (right), full-length dehydrogenase genes obtained by chemical synthesis are used directly in coupled transcription/translation reactions to obtain the proteins of interest.

Approaches to cloning DNA Genomic DNA Restriction endonucleases fragment DNA Total nuclear DNA cloned Genes contain introns cDNA Reverse transcription of mRNAs from cell Genes expressed cloned Genes have no introns... 

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