Construction of new vectors for cloning of promoters

Vectors for cloning promoter-DNA fragments were derived from plasmid pBR313 (Bolivar et al., 1977). These have several unique restriction sites and carry the trpA gene from Escherichia coli as a selective marker. The selection is based on an enhancement of the growth rate of those bacteria in which the expression of trpA is directed by the cloned promoter. The expression of trpA can be determined quantitatively, independently of the copy number of the vector, and should reflect the apparent strength of the promoter, since the DNA segment located before trpA contains translational stop signals in all three reading frames.     

含P_RP_L启动子的原核高效表达载体的组建及其应用

我们组建了一个含P_RP_L自动子的原核高效表达载体,它同时含有cI调控基因、多酶切点和两个强的转录终止序列。带起始密码子ATG的外源基因可以插入启动子下游的多酶切点,表达非融合蛋白,产品可供临床使用。我们实验室已用它成功地表达了人γ干扰素、人白细胞介素-2和人肿瘤坏死因子等,表达量均占菌体总蛋白的20％以上。     

Characterization of an immunoglobin cDNA clone containing the variable and constant regions for the MOPC 21 kappa light chain.

Nucleotide sequence analysis and restriction endonuclease mapping have been used to characterize a cDNA copy of immunoglobulin MOPC 21 Kappa mRNA clones in the bacterial plasmid pMB9. Three regions of the inserted cDNA of plasmid pL21-1 have been sequenced and match the known protein sequence at amino acid residues 1-24, 128-138 and 171-179. With these sequences to provide absolute correlations between the restriction map and the structural gene sequence it has been possible to exactly deduce the positions of all 11 of the insert restriction sites mapped within the structural gene. The pL21-1 insert contains the complete variable and constant regions as well as parts of the 3' untranslated and polypeptide leader coding sequences.     

A general method for inserting specific DNA sequences into cloning vehicles

A general method has been developed to introduce any double-stranded DNA molecule into cloning vehicles at different restriction endonuclease sites. In this method a chemically synthesized decadeoxyribonucleotide duplex, containing a specific restriction endonuclease sequence, is joinlex DNA is cut by the same restriction endonuclease to generate the cohesive ends. It is then inserted into the restriction endonuclease cleavage site of the cloning vehicle. To demonstrate the feasibility of this new method, we have inserted separately the synthetic lac operator DNA at the Bam I and HindIII cleavage sites of the plasmid pMB9 DNA.     

Improved plasmid vectors with a thermoinducible expression and temperature-regulated runaway replication

Improved expression vectors have been constructed which are derived from runaway-replication mutants of plasmid R1 and carry the strong leftward promoter (pL) of bacteriophage lambda. The activity of this promoter is controlled by a temperature-sensitive repressor, product of the phage gene cI cloned on a compatible plasmid. Heat induction leads to amplification of the plasmid copy number and at the same time turns on the promoter. At a short distance downstream from the promoter, unique EcoRI, BamHI, XbaI and HindIII sites are present. This system was used for high level expression of the T4 DNA-ligase gene; 3 h after induction the ligase amounted to about 20% of total cellular protein.     

Construction and characterization of new cloning vehicles. I. Ampicillin-resistant derivatives of the plasmid pMB9.

In vitro recombination via restriction endonucleases and the in vivo genetic translocation of the Ap resistance (Apr) gene resulted in the construction of a new cloning vehicle, the plasmid pBR313. This vector was derived from a ColE1-like plasmid and, while it does not produce colicon E1, it still retains colicin E1 immunity. The Apr and tetracycline resistance (Tcr) markers carried in pBR313 were derived from the ampicillin transposon (TnA) of pRSF2124 and pSC101 respectively. During the construction of pBR313, the TnA component was altered and the Apr gene in pBR313 can no longer be translocated. This plasmid has a molecular weight of 5.8 Mdalton and has been characterized using thirteen restriction enzymes, six of which (EcoRI, SmaI, HpaI, HindIII, BamHI and SalI) cleave the plasmid at unique restriction sites. This allows the molecular cloning of DNA fragments generated by these six enzymes. The restriction sites for the latter three enzymes, HindIII, BamHI and SalI, are located in the Tcr gene(s). Cloning DNA fragments into these sites alters the expression of the Tcr mechanisms thus providing a selection for cells carrying recombinant plasmid molecules. An enrichment method for AprTcS cells carrying recombinant plasmid molecules is described.     

High-level expression vectors to synthesize unfused proteins in Escherichia coli

A new class of plasmid vectors (pANK-12, pANH-1, and pPL2) for synthesizing unfused proteins was constructed by inserting synthetic linkers at the NdeI site (CATATG) of plasmid pJL6, which contains the lambda cII gene initiator codon. These expression vectors contain the lambda pL promoter, the cII ribosome-binding site, cII start codon and unique restriction sites (KpnI, Asp718, HpaI, BamHI) downstream from the initiator ATG for expression of unfused proteins. The main advantage of these vectors is that any DNA fragment with an open reading frame that does not possess a start and/or a stop codon can be directed to overproduce protein in an unfused form.     

Plasmid vehicles for direct cloning of Escherichia coli promoters.

A multicopy plasmid cloning vehicle, pGA22, which carries genes for ampicillin resistance (Apr), tetracycline resistance (Tcr), chloramphenicol resistance (Cmr), and kanamycin resistance (Kmr) has been constructed. This plasmid has five unique sites for restriction endonucleases EcoRI, PstI, XhoI, SmaI, and SalI within antibiotic resistance genes. pGA22, which is 5.1 megadaltons in size, has a low copy number (probably fewer than 10 per genome), is capable of relaxed replication, and is mobilized by F-factor at a frequency of 10(-5). A series of promoter-cloning vehicles, pGA24, pGA39, and pGA46, has been developed from pGA22. In these plasmids the natural promoter for Tcr has been removed and has been replaced by small deoxyribonucleic acid fragments carrying unique sites for several restriction endonucleases. Cells carrying these vectors are sensitive to tetracycline unless insertional activation of the Tcr occurs by cloning a promoter-carrying deoxyribonucleic acid fragment in one of the unique sites adjacent to the 5' end of Tcr. In this way, promoters carried on a HindIII-generated deoxyribonucleic acid fragment can be inserted at the HindIII site of plasmid pGA24, pGA39, or pGA46. A promoter in fragments generated by digestion with restriction endonuclease XmaI or PstI or by any restriction endonucleases which generate flush ends, such as SmaI, PvuII, HpaI, HincII, or HaeIII, can be clones in plasmid pGA39. Plasmid pGA46 can be used to detect a promoter fragment carried on a BglII, BamHI, MboI, or PstI fragment. We also describe a plasmid, pGA44, with a unique KpnI site in the rifampin resistance gene rpoB.     

Construction of a DNA-polymerase I overproducing plasmid and isolation of the enzyme

The polA gene of Escherichia coli coding for DNA polymerase I was cloned under the control of bacteriophage lambda promoter pL and gene N in a high copy number plasmid vector. The chromosomally located lambda cIts repressor gene kept the synthesis of the polA gene product at 28 degrees C at a low level. Raising the temperature to 43 degrees C resulted in inactivation of the repressor and overproduction of DNA polymerase I, which could easily be purified to homogeneity.