title: Recombination-stable multimeric green fluorescent protein for characterization of weak promoter outputs in Saccharomyces cerevisiae.
abstract: Green fluorescent proteins (GFPs) are widely used for visualization of proteins to track localization and expression dynamics. However, phenotypically important processes can operate at too low expression levels for routine detection, i.e. be overshadowed by autofluorescence noise. While GFP functions well in translational fusions, the use of tandem GFPs to amplify fluorescence signals is currently avoided in Saccharomyces cerevisiae and many other microorganisms due to the risk of loop-out by direct-repeat recombination. We increased GFP fluorescence by translationally fusing three different GFP variants, yeast-enhanced GFP, GFP+ and superfolder GFP to yield a sequence-diverged triple GFP molecule 3vGFP with 74-84% internal repeat identity. Unlike a single GFP, the brightness of 3vGFP allowed characterization of a weak promoter in S. cerevisiae. Utilizing 3vGFP, we further engineered a less leaky Cu(2+)-inducible promoter based on CUP1. The basal expression level of the new promoter was approximately 61% below the wild-type CUP1 promoter, thus expanding the absolute range of Cu(2+)-based gene control. The stability of 3vGFP towards direct-repeat recombination was assayed in S. cerevisiae cultured for 25 generations under strong and slightly toxic expression after which only limited reduction in fluorescence was detectable. Such non-recombinogenic GFPs can help quantify intracellular responses operating a low copy number in recombination-prone organisms.
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kogle Allé 6, DK-2970 Hørsholm, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Rugbjerg
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kogle Allé 6, DK-2970 Hørsholm, Denmark.
authors.forename: Christoph
authors.initials: C
authors.lastname: Knuf
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kogle Allé 6, DK-2970 Hørsholm, Denmark.
authors.forename: Jochen
authors.initials: J
authors.lastname: Förster
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kogle Allé 6, DK-2970 Hørsholm, Denmark msom@bio.dtu.dk.
authors.forename: Morten O A
authors.initials: MO
authors.lastname: Sommer
mesh_terms: D019677:Artificial Gene Fusion; D020869:Gene Expression Profiling / Q000379:methods*; D005827:Genetics, Microbial / Q000379:methods*; D042822:Genomic Instability; D049452:Green Fluorescent Proteins / Q000032:analysis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000032:analysis / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins
keywords: promoter engineering; protein multimerization; signal amplification; synthetic biology