A 2.1-kb DNA fragment containing the SWA2 gene determining an alpha-amylase from Schwanniomyces occidentalis has been sequenced. It contains an open reading frame of 1521 bp which has the potential to encode a 507 amino-acid protein of M(r) 55966. Its deduced amino-acid sequence shows significant similarities to the sequence of other studied alpha-amylases. These similarities identify a consensus sequence, F(LIV)(ED)NHD, which is shared in addition by most maltases, invertases and glucoamylases.

The effect of different carbon sources on the expression in Saccharomyces cerevisiae of the SWA2 alpha-amylase gene from Schwanniomyces occidentalis was studied from constructs containing its 5' region (-223 to +15), which were fused in-frame to the lacZ gene coding sequence. Maximal expression was achieved with the non-fermentable substrates ethanol and/or glycerol, whereas lower levels were found with maltose or galactose. In contrast, glucose repressed it, even in the presence of any of these other carbon sources. Deletion analyses of the -233 to -85 SWA2 promoter region permitted the identification of two fragments involved in both glucose repression and ethanol activation. A possible region required for cAMP regulation was localised. The SWA2 promoter contains a MIG1-binding GC box whose deletion caused a five-fold increase in the glucose-repressed reporter expression. Despite this, expression of the SWA2 promoter was not MIG1-dependent.