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2‐μm vectors containing the Saccharomyces cerevisiae metallothionein gene as a selectable marker: Excellent stability in complex media, and high‐level expression of a recombinant protein from a CUP1 ‐promoter‐controlled expression cassette in cis
Author(s) -
Hottiger Thomas,
Kuhla Jochen,
Pohlig Gabriele,
Fürst Peter,
Spielmann Albert,
Garn Morten,
Haemmerli Stephan,
Heim Jutta
Publication year - 1995
Publication title -
yeast
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.923
H-Index - 102
eISSN - 1097-0061
pISSN - 0749-503X
DOI - 10.1002/yea.320110102
Subject(s) - biology , plasmid , selectable marker , expression vector , expression cassette , saccharomyces cerevisiae , microbiology and biotechnology , metallothionein , gene , marker gene , shuttle vector , vector (molecular biology) , recombinant dna , genetics
We have constructed 2‐μm‐based yeast expression vectors containing a copy of the metallothionein ( CUP1 ) gene of Saccharomyces cerevisiae as a semi‐dominant, selectable marker. When used for the expression of the thrombin inhibitor hirudin, originally derived from the leech Hirudo medicinalis , these vectors displayed the following characteristics. (1) In the presence of copper salts, they were mitotically more stable than similarly designed control vectors lacking the CUP1 gene. In copper‐sensitive host strains, the apparent plasmid stability was 100%, even in complex media and during fed‐batch fermentation for an extended period of time. (2) Use of the CUP1 ‐stabilized plasmids improved the production of hirudin by both copper‐sensitive and copper‐resistant hosts. The highest hirudin titers were obtained with a Δ CUP1 host. (3) Copper selection resulted in a moderate increase in average plasmid copy numbers (up to two‐fold) as assessed by measuring hirudin expression from a constitutive promoter (GAPFL). This effect was most noticeable if the vector showed an asymmetric segregation pattern (i.e., high rates of plasmid loss in the absence of copper). (4) The CUP1 marker proved particularly useful in combination with a CUP1 ‐promoter‐controlled expression cassette on the same plasmid. In such a set‐up, the rates of transcription of the heterologous protein and that of the selectable marker are tightly linked. Therefore, an increase in selective pressure directly provokes an increase in product yields. In a copper‐sensitive host strain, this plasmid design allowed for the production of very high amounts of biologically active hirudin. Our results clearly establish the utility of the CUP1 marker in the construction of stable yeast expression vectors.