NOVELTY - Yeast cell, which produces isobutanol, is new, where: the cell has an increased metabolic flow of material from pyruvate, acetolactate, 2,3-dihydroxy isovalerate, 2-ketoisovalerate, isobutyraldehyde to isobutanol; at least one of the genes coding the enzymes, which are involved in the conversion, is over-expressed, and none of the genes is heterologous to the yeast cell; and either at least one of the promoters of the genes is exchanged against at least one stronger promoter or the nucleic acid sequences of the genes are modified into codon-optimized alleles.    USE - The yeast cell is useful for producing isobutanol, which is useful as: fuels; basic chemical for the production of other chemicals; or solvent.    ADVANTAGE - The additional mutation in the yeast cell increases the production of isobutanol and increases the resistance against toxic concentration of isobutanol.    DETAILED DESCRIPTION - Yeast cell, which produces isobutanol, is new, where: the cell has an increased metabolic flow of material from pyruvate, acetolactate, 2,3-dihydroxy isovalerate, 2-ketoisovalerate, isobutyraldehyde to isobutanol; at least one of the genes coding the enzymes, which are involved in the conversion, is over-expressed, and none of the genes is heterologous to the yeast cell; Ilv2 (YMR108W) (SEQ. ID. No. 2) catalyzes the acetolactate synthesis reaction from pyruvate to acetolactate, Ilv5 (YLR355C) (SEQ. ID. No. 6) catalyzes the acetohydroxy acid reductoisomerase reaction from acetolactate to 2,3-dihydroxy isovalerate, Ilv3 (YJR016C) (SEQ. ID. No. 8) catalyzes the dihydroxy acid dehydratase reaction from 2,3-dihydroxy isovalerate to 2-ketoisovalerate, a 2-keto acid decarboxylase catalyzes the reaction from 2-ketoisovalerate to isobutyraldehyde, and an alcohol dehydrogenase catalyzes the reaction from isobutyraldehyde to isobutanol; and either at least one of the promoters of the genes is exchanged against at least one stronger promoter or the nucleic acid sequences of the genes are modified into codon-optimized alleles, where the sequences not defined here may be found at ftp://ftp.wipo.int/pub/published_pct_sequences/publication. An INDEPENDENT CLAIM is included for a method for producing isobutanol with the yeast cell, comprising providing the yeast cell and contacting the cell with the fermentable carbon source.