product was made with a strain of E. coli. Most bacteria, including E. coli, are unable to successfully secrete such proteins, requiring added cell harvesting, cell disruption, and product isolation steps before protein purification. Like Humulin, there have been many successes using heterologous expression for drug development. Heterologous expression via cloning of genes producing natural bioactive products of interest also can be expressed in host systems and scaled up for drug production. For example, several clinically relevant natural products in fungi are difficult to culture in laboratory settings. However, after identification of the corresponding active gene clusters, these genes can be cloned into yeast and expressed as well to produce the product of interest in a more cost and time effective way. This method can also be used to discover new drugs. In this experiment, previously unstudied fungal genetic sequences can be characterized and expressed, which allows the production of new natural products. However, with mutagenesis of genes towards a more biologically relevant compound, this can then be expressed to yield a new genetically modified product. Another important use of heterologous expression is to screen different drugs in a host system rather than a more expensive or difficult to sustain native system. An example of this would be using Mycobacterium marinum as an alternative host system compared to directly using Mycobacterium tuberculosis. M. tuberculosis requires high biosafety level facilities for drug screening and has a slow growth rate which makes the process expensive and time-consuming. Therefore, researchers tested a closely related and less hazardous M. marinum, which heterologous expression of two drug activators, became an accurate model to test tuberculosis drugs in. An example examining a more focused drug target is the heterologous expression of ion channel proteins to test different cardiac ion channel drugs that alter their function to address heart disease. Similarly, drug screening can occur with heterologous expression of cloned receptors. The benefits of using heterologous expression here is that it produces large amounts of target receptors of drugs of interest, and is generally inexhaustible, reproducible, and inexpensive. These receptors could then be used in assays to test the effectiveness and specificity of drug binding. Moreover, the produced receptors themselves could be used as therapeutics. They could serve as decoys for toxins or excess signaling molecules, and bind/attenuate these molecules Biofuels Recombinant technology has also played a role in biofuel development. This has been explored using expression