A fully modular vector system for the optimization of gene expression in Escherichia coli.

The new expression vector system CYTEXP is designed to facilitate the optimization of both transcription and translation in Escherichia coli, while at the same time allowing the exchange of its major components using unique restriction sites. In vitro mutagenesis can be performed in situ using single-stranded DNA generated from the bacteriophage f1 ORI sequence. The basic vector pCYTEXP1 bears a synthetic copy of the intercistronic sequence that enhances the translation of the E. coli atpE gene. Reading frames can be inserted directly downstream of this sequence. The bacteriophage lambda promoters, the atpE sequence, the bacteriophage fd transcriptional terminator, the f1 ORI, and the amp antibiotic resistance gene are all borne on exchangeable "modules." Thus, both the efficiency and the conditions of expression of cloned genes can be readily optimized.