pWITCH: a versatile two-hybrid assay vector for the production of epitope/activation domain-tagged proteins both in vitro and in yeast.

We describe the construction of a new vector, pWITCH, designed to facilitate the characterisation of proteins encoded by novel cDNAs isolated using either a one- or two-hybrid assay. Expression of directionally cloned cDNAs is directed in vivo in Saccharomyces cerevisiae from the inducible GAL10 promoter and in vitro from the T7 promoter, while translation of the expressed cDNAs results in proteins which are tagged in vitro with a specific epitope and in vivo with both the epitope and the VP16 transcription activation domain. The principle of using multiple promoters each able to operate under different conditions to express different combinations of protein domains without the need for subcloning should be generally applicable.