title: Development of a LAC4 promoter-based gratuitous induction system in Kluyveromyces lactis.
abstract: A gratuitous induction system based on the strong, indigenous LAC4 promoter was developed for Kluyveromyces lactis. To prevent consumption of the inducer galactose, a strain with a gal1-209 mutation was employed; this mutation disables the galactokinase function but retains the regulatory function for induction. The Escherichia coli lacZ gene (encoding beta-galactosidase) is functional in K. lactis and was used as the reporter gene downstream of the LAC4 promoter on a multicopy plasmid. The gal1-209 strain exhibited several unexpected phenomena, including partial consumption of the inducer galactose (although at a much slower rate relative to GAL1 strains) and growth inhibition at high concentrations of galactose. These unusual characteristics, however, did not prevent the successful construction of a strong gratuitous induction system. Due to the low rate of inducer consumption for the gratuitous strain, very low concentrations of galactose (1:20 galactose:glucose) resulted in high-level induction. Under these conditions, beta-galactosidase specific and volumetric activities were 4.2- and 5.5-fold higher, respectively, than those for the "GAL1" nongratuitous strain. This research demonstrated the improved productivity possible via LAC4 promoter-based gratuitous induction (and thus a more stable inducer concentration). The effects of various carbon source concentrations on growth and induction were also determined.
authors.affiliation: Department of Chemical and Biochemical Engineering & Materials Science, University of California, Irvine, California 92697-2575, USA.
authors.forename: H B
authors.initials: HB
authors.lastname: Hsieh
authors.forename: N A
authors.initials: NA
authors.lastname: Da Silva
mesh_terms: D002455:Cell Division; D005285:Fermentation; D005690:Galactose / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005818:Genetic Engineering / Q000379:methods*; D005947:Glucose / Q000378:metabolism; D007716:Kluyveromyces / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D001616:beta-Galactosidase; D005947:Glucose; D005690:Galactose