No abstract

No abstract

The induction of alpha-amylase by starch has been studied in the filamentous fungus Aspergillus oryzae. Low levels of alpha-amylase activity were found in both intracellular and extracellular samples from glucose-grown cultures. However, alpha-amylase activity increased when starch was the sole carbon source. The intracellular enzyme activity was induced by a factor of approximately 6.5, while the extracellular activity increased 20-fold over that found in the glucose-grown cultures. Regardless of the carbon source or cellular location, the molecular weight of the active protein was 52 500 +/- 1800 and only this protein reacted with antibodies specific for alpha-amylase. A parallel study of the in vitro translated proteins directed by poly(A)+ RNA fractions indicated a presumptive alpha-amylase with a similar isoelectric point but with a molecular weight of approximately 54 000. This protein was most prevalent using RNA from early, exponentially growing cultures in starch medium. Immunoprecipitation data indicate that the abundance of alpha-amylase transcripts decreases dramatically after the first 12 h, reflecting an initial transcription control for the expression of this enzyme.

Saccharomyces diastaticus produces an extracellular glucoamylase and is therefore capable of hydrolyzing and fermenting starch. Tamaki (1978) studied starch utilization in S. diastaticus and found three polymeric genes controlling this function: STA1, STA2 and STA3. Independently, Erratt and Stewart (1978) studied dextrin utilization by the yeast S. diastaticus and designated the gene, which they identified, DEX1. Erratt and Stewart (1981 a, b) later described two other genes which controlled glucoamylase production in S. diastaticus: DEX2 and a third which was allelic to STA3. At that time STA1 and STA2 were not available to test for allelism in the DEX gene family. In this study strains containing the remaining 4 genes have been examined to determine if further allelism exists between the two gene families. It was ascertained that DEX1 is allelic to STA2 and DEX2 is allelic to STA1. Therefore, no new gene controlling starch utilization has been identified and these two nomenclatures can now be consolidated into one. Based on the fact that the glucoamylase from S. diastaticus can hydrolyze both dextrin and starch, dextrin being the term used to describe partially hydrolyzed starch, and the more wide use of the nomenclature STA, we propose to retain STA as the designation for genes coding for glucoamylase production in S. diastaticus.

No abstract