THE S1, S2 AND SGA1 ANCESTRAL GENES FOR THE STA GLUCOAMYLASE GENES ALL MAP TO CHROMOSOME-IX IN SACCHAROMYCES-CEREVISIAE

The polymorphic extracellular glucoamylase-encoding genes STA1 (chr. I V), STA2 (chr. II) and STA3 (chr. XIV), from Saccharomyces cerevisiae var. diastaticus probably evolved by genomic rearrangement of DNA regi ons (S1, S2 and SGA1) present in S cerevisiae, and subsequent transloc ation to unlinked regions of chromosomal regions. S1, encoding a homol ogue to the threonine/serine-rich domain of STA glucoamylases (GAI-III ), mapped to the right arm of chormosome IX. S2, encoding the hydropho bic leader peptide of GAI-III, was also mapped on the right arm of chr omosome IX, next to S1, close to DAL81. The SGA1 sporulation-specific, intracellular glucoamylase-encoding gene is located on the left arm o f chromosome IX, 32 kb proximal of HIS5.