The role of the beta-lactamase signal sequence in the secretion of proteins by Escherichia coli

A derivative of pBR322 has been constructed that contains both a unique EcoRI restriction site right at the beginning of the signal codons of the beta-lactamase (bla) gene and a unique BstEII site just at the end of the bla signal codons. Although the signal peptide encoded by the new plasmid differs from the wild type (pBR322) by 2 amino acid residues (Ser 2 to Arg 2 and Ala 23 to Gly 23), the synthesis, transport, and processing of the beta-lactamase remain unchanged in Escherichia coli. Two deletion mutants, in which the bla signal codons have been almost completely excised, have also been constructed. Bacteria containing either of these plasmids produce, but do not secrete, an active beta-lactamase. Last, the bla signal codons have been precisely joined to the cDNA version of the triose phosphate isomerase (tpi) gene from chicken. Expression of this fusion gene in E. coli gives a hybrid protein that is neither secreted into the periplasm nor proteolytically processed. This result supports the view that there are characteristics of the mature protein that are necessary for the secretion across the inner membrane of E. coli.

Chemical synthesis of a human interferon-alpha 2 gene and its expression in Escherichia coli

A 511-base pair DNA fragment encoding human interferon-alpha 2 has been chemically synthesised and expressed from a lac UV5 and a synthetic trp promoter in Escherichia coli. The synthesis involved preparation of 68 oligodeoxyribonucleotides and their enzymic ligation. The product expressed from the trp promoter system had high antiviral activity and displayed biological effects similar to those of Namalwa interferon on natural killer cell activity and in a Daudi cell growth inhibition assay. E.coli minicells containing plasmid DNA with the synthetic IFN-alpha 2 gene under trp promoter control produce a protein with the same electrophoretic mobility as a sample of authentic IFN-alpha 2. The protein from E.coli cross-reacts with the monoclonal antibody NK-2 and was readily purified, close to homogeneity, by immunoadsorption chromatography on NK-2 sepharose.

Ion-exchange high-performance liquid chromatography of oligodeoxyribonucleotides using formamide

The superiority of buffer systems containing formamide for the ion-exchange high-performance liquid chromatographic separation of oligodeoxyribonucleotide mixtures generated in solid-phase syntheses is illustrated. The resolutions achieved are compared to those achieved with the same mixtures in other eluting solvents. The use of formamide systems is recommended for oligodeoxyribonucleotide purification in general and is particularly valuable where the oligonucleotide of interest is highly self-complementary and/or rich in deoxyguanosine residues.

The construction of a synthetic Escherichia coli trp promoter and its use in the expression of a synthetic interferon gene

An 82 base pair DNA fragment has been synthesised which contains the E. coli trp promoter and operator sequences and also encodes the first Shine Dalgarno sequence of the trp operon. This DNA fragment is flanked by EcoRI and ClaI/TaqI cohesive ends and is thus easy to clone, transfer between vector systems and couple to genes to drive their expression. It has been cloned into plasmid pAT153, producing a convenient trp promoter vector. We have also joined the fragment to a synthetic IFN-alpha 1 gene, using synthetic oligonucleotides to generate a completely natural, highly efficient bacterial translation initiation signal on the promoter proximal side of the IFN gene. Plasmids carrying this construction enable E. coli cells to express IFN-alpha 1 almost constitutively and with significantly higher efficiency than from a lacUV5 promoter based system.

Targeted point mutation that creates a unique Eco RI site within the signal codons of the beta-lactamase gene without altering enzyme secretion or processing

A method has been developed for constructing site-specific mutations by using a strongly selectable marker on which to "piggy-back" a desired mutation that may be phenotypically silent. Using this approach, a new unique Eco RI restriction site has been generated at the beginning of the signal codons of the beta-lactamase gene of the plasmid pBR322. The consequential alteration of the second amino acid of the signal from Ser to Arg has no effect on either the transport or the processing of the beta-lactamase.

Total synthesis of a human leukocyte interferon gene

A 514-base pair fragment of double-stranded DNA coding for human interferon-alpha 1 (166 amino acid residues), and containing initiation and termination signals plus appropriate restriction enzyme sites for plasmid insertion, has been totally synthesized. The synthesis involved preparation of 66 oligodeoxyribonucleotides, ranging in size from 14 to 21 residues, plus 1 deoxydecanucleotide, by rapid, solid phase procedures, and enzymatic ligation of the oligonucleotides. After ligation of the synthetic gene to a plasmid vector and transformation of Escherichia coli, clones containing the anticipated gene sequence were obtained.

Solid phase phosphotriester synthesis of large oligodeoxyribonucleotides on a polyamide support

Phosphotriester solid phase methodology on a polyamide support [(1980) Nucleic Acids Research, 8, 1081-1096] has been extended for the rapid synthesis of the tetradecanucleotide, d(AGTTGTTTGTAGTT), the octadecanucleotide, d(GTGGGTTTGGGGCAGGTC), and the heneicosanucleotide, d(GTGCTCTTATCCTCTTGGCTC). Thus, oligodeoxyribonucleotides comparable in size to those obtained by solution synthesis are readily accessible using solid phase techniques. An approach to the purification of the synthetic octadecanucleotide without recourse to high performance liquid chromatography is described.

Rapid synthesis of oligodeoxyribonucleotides. IV. Improved solid phase synthesis of oligodeoxyribonucleotides through phosphotriester intermediates

A phosphotriester solid phase method on a polyamide support has been used to prepare oligodeoxyribonucleotides up to 12 units long. Compared to solid phase phosphodiester synthesis the new methodology is quicker, more flexible and gives 10-60-fold better overall yields.