Sequence analysis of the α-galactosidase MEL gene governing the efficient production of ethanol from raffinose-rich molasses in the yeast Lachancea thermotolerans

The yeast Lachancea thermotolerans, formerly Kluyveromyces thermotolerans, was tested for the ethanol fermentation of raffinose-rich molasses. Two melibiose-fermenting strains, NBRC 10066 and NBRC 10067, produced more ethanol than eight other strains. The concentration of ethanol synthesized by NBRC 10066 was slightly higher than that by NBRC 10067, probably on the basis of the expression of alpha-galactosidase. The regions corresponding to the alpha-galactosidase MEL1 gene of Saccharomyces cerevisiae were amplified. The nucleotide sequences of the two genes designated as MELth1 and MELth2 revealed single open reading frames of 1,416 bp encoding 472 amino acids but differed from each other in one base that converted the amino acid composition. The sequences of the 5'-upstream region from -1 to -515 of the two genes are identical except for one base.