One general form of cell engineering involves altering natural cell production to achieve a more desirable yield or shorter production time. A possible method for changing natural cell production includes boosting or repressing genes that are involved in the metabolism of the product. For example, researchers were able to overexpress transporter genes in hamster ovary cells to increase monoclonal antibody yield. Another approach could involve incorporating biologically foreign genes into an existing cell line. For example, E.Coli, which synthesizes ethanol, can be modified using genes from Zymomonas mobilis to make ethanol fermentation the primary cell fermentation product.