Expression plasmid vectors containing Escherichia coli tryptophan promoter transcriptional units lacking the attenuator.

Two DNA fragments which contain the Escherichia coli tryptophan promoter operator region but lack the attenuator have been used in the construction of a series of pAT153 based plasmids suitable for the regulated expression of foreign genes in E. coli. The first, a 139-bp HhaI fragment includes 59 bp of the trp leader sequence, ending within the "attenuator peptide" coding sequence, eleven codons from the N-terminus. A fusion-type expression plasmid incorporating this fragment has been constructed. The second, a 99-bp HaeIII-TaqI fragment contains no coding sequence but includes the "attenuator peptide" SD site situated 4 bp upstream of the TaqI site. This fragment has been incorporated in expression vectors which result in the direct expression of cloned gene sequences. To further maximise expression, plasmids with directly repeating trp promoter HaeIII-TaqI units have been constructed.