Isolation and characterization of the Pichia stipitis transketolase gene and expression in a xylose-utilising Saccharomyces cerevisiae transformant.

The gene TKT from P. stipitis, encoding the enzyme transketolase (EC 2.2.1.1), was cloned from a genomic library by hybridization with a S. cerevisiae TKT1-gene-specific probe. The nucleotide sequence determined contains an open-reading frame of 2085 base pairs (bp) encoding a protein of 695 amino acids with a predicted molecular mass of 75113 Da. The TKT gene was actively expressed in S. cerevisiae when placed under the control of the homologous PDC1(-15) promoter and could complement a S. cerevisiae tkt deletion. The TKT protein was immunologically detectable using S. cerevisiae transketolase-specific antiserum. Overexpression of the P. stipitis TKT gene in a xylose-utilizing S. cerevisiae XYL1/XYL2 integrant led to a drastically extended generation time during growth on xylose minimal medium under aerobic conditions.