Plasmid vectors containing the tryptophan operon promoter suitable for efficient regulated expression of foreign genes

The construction of new vehicles for the cloning of transcription termination signals

We have constructed new plasmids that can be used to clone transcription terminator containing DNA fragments between the first gene of the tryptophan (trp) operon and the tetracycline resistance (tet) gene. Both genes are under control of the trp promotor. Therefore the presence of a transcription termination signal on cloned fragments can be monitored by a decrease in expression of the tet gene. The plasmids contain cloning sites at different distances from the translation start signal. Consequently a cloned DNA fragment can be translated in the three possible reading frames, offering the opportunity to distinguish terminators from translation polarity (pseudo-terminators). The usefulness of the plasmids was shown by the cloning of the trp terminator and of a pseudo-terminator located in the trpB gene.

The absence of introns within a human fibroblast interferon gene

Experiments in which immobilised restriction fragments of genomic DNA were hybridised with a cloned human fibroblast interferon cDNA indicate that the homologous chromosomal genes exist in only one basic arrangement. This is in marked contrast to recent studies by Nagata et al. (1) showing that there are at least eight gene arrangements for human leukocyte interferon. Having isolated a chromosomal human fibroblast interferon gene from a gene bank, we conclude from nucleotide sequencing studies that there is a complete absence of introns within the RNA-coding region. In view of a similar observation recently made for a human leukocyte interferon gene (1), it would appear as if interferon genes in general are unlike the vast majority of eukaryote genes in this respect.

The expression in E. coli of synthetic repeating polymeric genes coding for poly(L-aspartyl-L-phenylalanine)

Two dodecadeoxynucleotides of defined sequence have been synthesised by phosphotriester methodology. They can be polymerised to give a double stranded DNA which codes, when read in the correct phase, for the repeating dipeptide poly(aspartyl-phenylalanine). This polymeric DNA has been cloned in E. coli K12 using as vector a plasmid having a controllable bacterial promoter upstream of the insertion site. Clones containing genes coding for up to 150 repeats of (aspartyl-phenylalanine) have been isolated and characterised. The polymeric inserts appear to be stable over many generations and are expressed in E. coli under the control of the bacterial promoter, to give a polymer of phenylalanine and aspartic acid which may be broken down enzymically to yield aspartyl-phenylalanine.

The construction and characterisation of plasmid vectors suitable for the expression of all DNA phases under the control of the E. coli tryptophan promoter

A DNA fragment flanked in the E. coli genome by Hinf I sites and containing the E. coli tryptophan promoter-operator and nucleotides specifying the leader sequence and first seven amino acids of trp E, has been cloned in the Hind III site of pBR322 with the aid of Hind III linkers. The Hind III site upstream from the trp promoter in the transcriptional sense was deleted to generate a Hind III cloning vector, designated pWT111, suitable for the expression of cloned DNA sequences as fusion products. Derivatives of this plasmid were constructed, designated pWT121 and pWT131, whose Hind III cloning sites differ with respect to their translation phasing relative to the initiator ATG of the trp E gene. Both pWT121 and pWT131 have a higher copy number per cell than pWT111. The tetracycline genes of all three plasmids are under trp promoter control and could be used to monitor the transcription of foreign genes inserted at the Hind III site of the vectors.