NOVELTY - Producing ethanol comprises: genetically engineering an isolated or recombinant nucleotide sequence encoding a polypeptide sequence comprising a fully defined sequence of 885 amino acids of SEQ ID NO: 17, a fully defined sequence of 891 amino acids each of SEQ ID NOs: 20 or 42, or a fully defined sequence of 360 amino acids of SEQ ID NO: 43, as given in the specification into a host cell; culturing the host cell to produce ethanol; and removing the ethanol.    USE - The method is useful for: producing ethanol; improving pyruvate decarboxylase activity, alcohol dehydrogenase activity (all claimed); and optimizing expression of alcohol dehydrogenase and pyruvate decarboxylase in host cells.    ADVANTAGE - The method: provides improved pyruvate decarboxylase enzyme, alcohol dehydrogenase enzyme, or bi-functional alcohol dehydrogenase enzyme, where improved activities comprises substrate affinity, substrate specificity, substrate catalytic conversion rate, improved thermostability, activity at a different pH or optimized codon usage for improved expression in a host cell; provides isolated nucleic acid molecules having pdc, adh1 or adh2 or adhE gene activity; provides genes which can be expressed at high levels in a range of organisms; and produces ethanol efficiently and cleanly.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) producing ethanol comprising genetically engineering an isolated or recombinant nucleotide sequence comprising fully defined sequences of 1014-2676 bps of SEQ ID NOs: 3, 6, 9, 12, 15, 16, 18, 19, 21, 23, 29, or 33, as given in the specification, into a host cell, culturing the host cell to produce ethanol and removing the ethanol;    (2) an isolated or recombinant polynucleotide comprising a nucleic acid sequence of any one of the sequences as given in the table 17 of the specification, a nucleic acid sequence that is a degenerate variant of any one of the sequences as in table 17; a nucleic acid sequence at least 95%, preferably 99.9% identical to any one of the sequences as in table 17 and a nucleic acid sequence that hybridizes under stringent conditions to any one of the sequences as in table 17;    (3) a vector comprising the isolated or recombinant polynucleotide;    (4) a fusion protein comprising any one of the polypeptide sequences as given in the table 16 of the specification, fused to a heterologous amino acid sequence;    (5) a host cell comprising the isolated or recombinant polynucleotide;    (6) an isolated antibody or antigen-binding fragment or its derivative which binds selectively to the isolated polypeptide;    (7) improving pyruvate decarboxylase activity comprising modifying a pyruvate decarboxylase gene employing rational design, error prone PCR, site-directed mutagenesis, whole gene site saturation mutagenesis, site-directed site saturation mutagenesis, gene shuffling or correlated site saturation mutagenesis, expressing the pyruvate decarboxylase gene in a host cell and screening the host cell for pyruvate decarboxylase activity;    (8) an improved pyruvate decarboxylase enzyme;    (9) improving alcohol dehydrogenase activity comprising: modifying a gene for alcohol dehydrogenase by employing rational design, error prone PCR, site-directed mutagenesis, whole gene site saturation mutagenesis, site-directed site saturation mutagenesis, gene shuffling or correlated site saturation mutagenesis; expressing the alcohol dehydrogenase gene in a host cell; and screening the host cell for alcohol dehydrogenase activity;    (10) an improved alcohol dehydrogenase enzyme;    (11) improving alcohol dehydrogenase activity comprising: modifying a gene for bi-functional alcohol dehydrogenase by employing rational design, error prone PCR, site-directed mutagenesis, whole gene site saturation mutagenesis, site-directed site saturation mutagenesis, gene shuffling or correlated site saturation mutagenesis; expressing the bi-functional alcohol dehydrogenase gene in a host cell; and screening the host cell for bi-functional alcohol dehydrogenase activity; and    (12) an improved bi-functional alcohol dehydrogenase enzyme.