TGATG vector: a new expression system for cloned foreign genes in Escherichia coli cells.

A TGATG vector system was developed that allows for the construction of hybrid operons with partially overlapping genes, employing the effects of translational coupling to optimize expression of cloned cistrons in Escherichia coli. In this vector system (plasmid pPR-TGATG-1), the coding region of a foreign gene is attached to the ATG codon situated on the vector, to form the hybrid operon transcribed from the phage lambda PR promoter. The cloned gene is the distal cistron of this hybrid operon ('overlappon'). The efficiently translated cro'-cat'-'trpE hybrid cistron is proximal to the promoter. The coding region of this artificial fused cistron [the length of the corresponding open reading frame is about 120 amino acids (aa)] includes the following: the N-terminal portions of phage lambda Cro protein (20 aa), the CAT protein of E. coli (72 aa) and 3' C-terminal codons of the E. coli trpE gene product. At the 3'-end of the cro'-cat'-'trpE fused cistron there is a region for efficient translation reinitiation: a Shine-Dalgarno sequence of the E. coli trpD gene and the overlapping stop and start codons (TGATG). In this sequence, the last G is the first nucleotide of the unique SacI-recognition site (GAGCT decreases C) and so integration of the structural part of the foreign gene into the vector plasmid may be performed using blunt-end DNA linking after the treatment of pPR-TGATG-1 with SacI and E. coli DNA polymerase I or its Klenow fragment.(ABSTRACT TRUNCATED AT 250 WORDS)