Human proteins can now be produced in bacteria such as E ....

Human proteins can now be produced in bacteria such as $E .$ coli. However, one cannot simply introduce a human gene into $E .$ coli and expect it to be expressed. What steps must be taken to construct an $E .$ coli strain that will produce a mammalian protein such as human growth hormone?

Key Concepts

Promoter and Regulatory Sequences

For the gene to be transcribed by the host’s RNA polymerase, bacterial promoter sequences and other regulatory elements (such as ribosome-binding sites) must be appropriately positioned. These elements control the initiation and efficiency of transcription and translation in the host bacteria.

Heterologous Gene Expression

This concept involves expressing a gene from one organism (e.g., a mammal) in a different host organism (e.g., a bacterium). It requires understanding the differences in gene regulation, transcription, and translation machinery between the donor and host organisms and making appropriate modifications to achieve proper expression.

cDNA Synthesis

Mammalian genes typically contain introns which bacteria cannot process. By converting mRNA into cDNA, the introns are removed, resulting in an intron-free gene sequence that can be properly expressed in prokaryotic systems.

Codon Optimization

Different organisms have preferences for certain codons that translate into the same amino acids. Optimizing the gene’s coding sequence to match the host organism's preferred codon usage can enhance translation efficiency, leading to higher levels of protein expression.

Vector Construction

This involves designing and constructing an expression vector that carries the modified gene along with the necessary regulatory elements. The vector must be suitable for replication and expression in the bacterial host, often including features such as selection markers, origin of replication, and multiple cloning sites.

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