Threonine Overproduction in Yeast Strains Carrying theHOM3-R2 Mutant Allele under the Control of Different Inducible Promoters

María-José Farfán; Luis Aparicio; Isabel L. Calderón

Threonine Overproduction in Yeast Strains Carrying theHOM3-R2 Mutant Allele under the Control of Different Inducible Promoters

Departamento de Genética, Facultad de Biologı́a, Universidad de Sevilla, E-41080 Seville, Spain

ABSTRACT

The HOM3 gene of Saccharomyces cerevisiaecodes for aspartate kinase, which plays a crucial role in the regulation of the metabolic flux that leads to threonine biosynthesis. With the aim of obtaining yeast strains able to overproduce threonine in a controlled way, we have placed the HOM3-R2 mutant allele, which causes expression of a feedback-insensitive enzyme, under the control of four distinctive regulatable yeast promoters, namely, P_GAL1, P_CHA1, P_CYC1-HSE2, and P_GPH1. The amino acid contents of strains bearing the different constructs were analyzed both under repression and induction conditions. Although some differences in overall threonine production were found, a maximum of around 400 nmol/mg (dry weight) was observed. Other factors, such as excretion to the medium and activity of the catabolic threonine/serine deaminase, also affect threonine accumulation. Thus, improvement of threonine productivity by yeast cells would probably require manipulation of these and other factors.

FOOTNOTES

Received 22 July 1998.
Accepted 16 October 1998.

↵* Corresponding author. Mailing address: Departamento de Genética, Facultad de Biologı́a, Universidad de Sevilla, Ap. 1095, E-41080 Sevilla, Spain. Phone: 34-954557108. Fax: 34-954557104. E-mail: genilc{at}cica.es.