Expression vectors are vectors that allow one to construct gene fusions that replace the native promoter of a gene with another promoter for any of a variety of reasons. For example, the native promoter might initiate transcription at a very low rate, too low to allow for purification or detection of the protein product of the gene, or only under very special conditions. Placing the ORF of the gene of interest under the control of a high-level constitutive promoter in a YEp vector would increase expression of the protein hopefully to levels that would allow the researcher to purify and characterize the product.
Several expression vectors are available to the Saccharomyces researcher and can be obtained from colleagues or from commercial sources. The ADH1 promoter is commonly used for high-level constitutive expression in glucose-grown cells. GAL1 and GAL10 are frequently used when regulated expression is desired. The GAL1 and GAL10 are induced to very high levels in galactose grown cells but expression is dramatically repressed by growth on glucose.
An expression system developed by Mumberg et al. (1995) allows for the constitutive production of a gene product over a 1000-fold range. One can choose from the promoters of either CYC1 encoding cytochrome-c oxidase isoform 1, ADH1 encoding alcohol dehydrogenase 1, TEF2 encoding translation elongation factor la, or GPD1 encoding glyceraldehyde-3-phosphate dehydrogenase. These are available in either YEp or YRp vectors, which provides another mechanism for varying the expression level. Additionally, one can choose from either HIS3, LEU2, URA3, or TRP1 as the selectable marker. If one prefers to be able to regulate the expression of the gene of interest, Labbe & Thiele (1999) developed a similar vector series but use the CUP1, CTR1, and CTR3 copper-regulated promoters.
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