TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Yeast: The heterologous gene alone encodes and expresses the enzyme for the metabolic pathway capable of utilizing NADH to convert acetyl-CoA to the n-butanol. The heterologous gene in combination with a native yeast gene encodes and expresses the enzyme for the metabolic pathway capable of utilizing NADH to convert acetyl-CoA to the n-butanol. The yeast overexpresses a pyruvate decarboxylase (PDC) to increase the production of cytosolic acetyl-CoA. The PDC is encoded by Saccharomyces cerevisiae gene PDC1. The PDC is encoded by S. cerevisiae gene PDC1, PDC5, and PDC6. The yeast overexpresses an aldehyde dehydrogenase (ALD) to increase production of cytosolic acetyl-CoA. The aldehyde dehydrogenase is encoded by S. cerevisiae gene ALD6. The ALD is encoded by Kluyveromyces lactis gene ALD6. The yeast overexpresses acetyl-CoA synthetase (ACS) to increase production of cytosolic acetyl-CoA. ACS is encoded by S. cerevisiae gene ACS1 and S. cerevisiae gene ACS2. The acetyl-CoA synthetase is encoded by K. lactis gene ACS1 and K. lactis gene ACS2. The yeast overexpresses both ALD and ACS to increase production of cytosolic acetyl-CoA. ALD is encoded by S. cerevisiae gene ALD6, and the ACS is encoded by S. cerevisiae gene ACS1 and S. cerevisiae gene ACS2. The yeast overexpresses a PDC encoded by Escherichia coli genes aceE, aceF, IpdA so as to increase production of cytosolic acetyl-CoA. The PDC activity is reduced and eliminated. The yeast overexpresses a PDC encoded by N-terminal mitochondrial targeting signal deleted S. cerevisiae genes PDAI, PDBI, PDXI, LATI, LPDI so as to increase production of cytosolic acetyl-CoA. The yeast is S. cerevisiae of genotype pdc2 delta and genotype pdc1 delta , genotype pdc5 delta , and genotype pdc6 delta . The yeast is K. lactis of genotype pdc1 delta . The yeast overexpresses both a pyruvate formate lyase and a formate dehydrogenase to increase the production of cytosolic acetyl-CoA. The yeast overexpresses a pyruvate formate lyase encoded by E. coli gene pflA and E. coli gene pflB, and in combination with Candida boidini gene formate dehydrogenase 1 to increase production of cytosolic acetyl-CoA. The heterologous gene has been subjected to molecular evolution to enhance the enzymatic activity of the protein encoded. The additional gene encoding alcohol dehydrogenase (ADH) is inactivated so that ADH activity is reduced to increase cytosolic acetyl-CoA production relative to wild-type production. The yeast is S. cerevisiae and K. lactis and ADH are encoded by ADH1. The yeast is K. lactis, and the ADH is encoded by ADH1. The yeast is S. cerevisiae, and the ADH is encoded by ADH1, ADH2, ADH3 and ADH4. The yeast is K. lactis, and the ADH is encoded by ADHI, ADHII, ADH1I1 and ADHIV. The yeast is a species from a genus of Saccharomyces, Dekkera, Pichia, Hansenula, Yarrowia, Aspergillus, Kluyveromyces, Pachysolen, Schizosaccharomyces, Candida, Trichosporon, Yamadazyma, Torulaspora, and Cryptococcus. The pathway provides for balanced NADH production and consumption when metabolizing the carbon source to produce n-butanol. The yeast is of the genus Kluyveromyces, the pyruvate decarboxylase is encoded by K. lactis gene KIPDC1, ALD is encoded by K. lactis gene KIALD6 and ACS is encoded by K. lactis genes KIACS1 and KIACS2. The ADH is inactivated by the deletion of K. lactis gene ADH1. EXAMPLE - Crude yeast protein extracts were made by a rapid TCA precipitation protocol. One 0D600 equivalent of cells was collected and treated with 200 mu l of 1.85 N sodium hydroxide/7.4% 2-mercaptoethanol on ice for 10 minutes. 200 mu l of 50% TCA was added and the samples incubated on ice for an additional 10 minutes. The precipitated proteins were collected by centrifugation at 25000 rcf for 2 minutes and washed with 1 ml of ice cold acetone. The proteins were again collected by centrifugation at 25000 rcf for 2 minutes. The pellet was then resuspended in sodium dodecyl sulfate (SDS) Sample Buffer and boiled (99 degrees C) for 10 minutes. The samples were centrifuged at maximum in a microcentrifuge for 30 seconds to remove insoluble matter.