Synthesis of proteins coded by plasmid vectors of pCV series (Apr, Tcr) and their recombinant derivatives (pDm) in E. coli minicells

Overexpression and purification of enzymatically active recombinant integrase protein of Rous sarcoma virus

The carboxy-terminal domain of polymerase gene of Rous sarcoma virus was cloned into an expression vector under the control of lac regulatory elements, resulting in the plasmid pMF1413. Upon isopropyl-beta-D-thiogalactopyranoside induction, viral integration (IN) protein was expressed in large quantity in Escherichia coli. The expressed recombinant protein was prepurified by successive washing of the bacterial pellet with 0.1 M NaCl and detergents. Further purification was performed in high yield by standard chromatography methods. The purified enzyme revealed selective DNA cleaving activity on supercoiled plasmid with the LTR-LTR junction fragment. The reaction was metal ion dependent, with a preference for Mn2+ over Mg2+, and showed substrate specificity at 1 mM MnCl2.

Leakage of periplasmic proteins from Escherichia coli mediated by polymyxin B nonapeptide

The effects of polymyxin B and polymyxin B nonapeptide (PMBN) on cell envelope integrity in Escherichia coli were compared. Both compounds caused loss of proteins from E. coli K-12 3300(pBR322), although PMBN released less protein than did polymyxin B. The origin of the released protein was determined both by polyacrylamide gel electrophoresis and by using specific enzyme markers (beta-lactamase in periplasm, beta-galactosidase in cytoplasm). The proteins released by both compounds were derived principally from the periplasm, accompanied in the case of polymyxin B by a low level of cytoplasmic proteins. Although polymyxin B and PMBN both caused release of periplasmic proteins, the individual proteins released by the compounds differed. The periplasmic fraction contained six principal polypeptides with molecular weights between 62,000 (polypeptide 1) and 29,000 (polypeptide 6). Polypeptide 6 was identified as the pBR322-encoded beta-lactamase, but the other proteins were not specifically identified. Polymyxin B caused considerable release of polypeptides 1, 2, and 5 with some release of polypeptides 4 and 6. PMBN released polypeptide 1 (trace), 3, 4, and 6 (trace). Scanning electron microscopy showed that polymyxin B and PMBN both caused surface damage in E. coli. However, polymyxin B produced greater morphological changes than PMBN.

Coliphage P2 late control gene ogr. DNA sequence and product identification

The bacteriophage P2 late control gene ogr was cloned and precisely localized by deletion analysis in vitro. The DNA sequence of the ogr gene containing the ogr1 mutation was determined. The sequence translates into a basic protein of a molecular weight of 8300. Plasmids overproducing the ogr gene product were constructed, and the ogr gene product was identified by polyacrylamide gel electrophoresis.

Expression of recombinant DNA functional products in Escherichia coli anucleate minicells

This review covers the use of anucleate minicells of Escherichia coli for expressing the recombinant DNA encoded proteins. We briefly discuss the methods being used for preparation of anucleate minicells, incorporation of cloned DNA and assessment of gene expression. While the largest use has been that of microbially derived cloned functional DNA, examples of eukaryotic gene product synthesis have also been reviewed. This technology may represent some interesting commercial opportunities.

Cloning of the Escherichia coli recJ chromosomal region and identification of its encoded proteins

A 9.6-kilobase BamHI-SalI fragment carrying recJ+ was cloned into vector pBR322. Deletion and transposon mutagenesis were used to map the recJ gene on this fragment. The maxicell protein-labeling technique was used to correlate a functional recJ gene with the presence of a polypeptide of 53,000 apparent molecular weight. Two additional genes, one encoding two proteins of 26,000 and 25,000 Mr and the other encoding a 31,000-Mr protein, were mapped on a 3.7-kilobase HindIII-SalI subfragment with recJ. Functions for these adjacent genes are not known; however, insertion mutations in these genes lessen the expression of the putative recJ protein detected in maxicells. A 9.6-kilobase BamHI-SalI fragment carrying the temperature-sensitive mutation recJ147 was also cloned and used for complementation studies to identify other recJ mutations.

Mutagenic SOS repair of site-specific psoralen damage in plasmid pBR322

The mutagenic repair of psoralen damage was examined by transforming Escherichia coli with psoralen-treated pBR322. Plasmid DNA randomly reacted with psoralen was repaired only when the E. coli was uvrA+ and recA+, and only when the cells were pre-irradiated with far-ultraviolet light. The recA dependence and requirement for pre-irradiation are characteristics of SOS repair. Psoralens were placed specifically near the BamHI site, in the tetracycline-resistance gene of pBR322, using a sulfhydryl-containing psoralen derivative. Repair of this damage also required pre-irradiation of the host cells. This repair was accompanied by a 4% frequency of mutagenesis to a tetracycline-sensitive phenotype. Sequence analysis of these mutant plasmids revealed that 75% had mutations within the targeted region, while 25% had no sequence changes within 100 bases of the BamHI site. In up to five independent isolates only one kind of mutation was observed at each site, suggesting that mutagenic SOS repair is influenced by DNA structure at the site of the psoralen. Most mutations were transitions, primarily G-C to A-T changes. Some transitions occurred at sites where psoralen crosslinks could not have formed, and these may have arisen from the repair of psoralen monoadducts.

Properties and products of the cloned int gene of bacteriophage P2

Fragments of DNA of the temperate phage P2, generated by treatment with the restriction enzyme PstI, have been cloned into the plasmid pBR322. One such fragment, which has its endpoints within phage genes T and C, carries the structural P2 int gene as well as its promoter and the phage att site. When introduced into a suitable bacterial host, the cloned fragment mediates the integration and excision of int- mutants of P2 and recombination within the phage att site in mixed infection. All these activities are independent of the orientation of the fragment within the plasmid. When introduced into minicells, the fragment produces, in addition to the products of genes D and U, a protein of 35-37,000 daltons identified as the int protein. A study of the map location of two amber int mutants, together with the sizes of the polypeptides they produce, indicates that the P2 int gene is transcribed from right to left on the P2 map, i.e. starting near gene C and proceeding toward att.

Cloning and deletion mapping of the recF dnaN region of the Escherichia coli chromosome

By cloning a 3.6-kb EcoRI fragment of the Escherichia coli chromosome with pBR322 we located more precisely recF relative to dnaN. By deletion mapping we localized functional recF to a 1.65-kb region of the cloned fragment and allowed rough mapping of the C terminus of dnaN. Cloned recF+, separated from functional flanking genes dnaN and gyrB, complemented chromosomal recF mutations presumably by coding for a cytodiffusible product. The protein encoded by dnaN was observed as a band on a polyacrylamide gel from minicells. Identification of a recF protein was not made.

Detection and mapping of six miniF-encoded proteins by cloning analysis of dissected miniF segments

Various DNA subfragments were derived from miniF DNA by complete or partial PstI cleavage, and cloned in the plasmid vectors pBR322 or lambda dv1. The recombinant plasmids obtained were introduced into an Escherichia coli minicell-producing strain, and the plasmid-coded proteins were radiolabeled and analyzed by gel electrophoresis. Six miniF-encoded proteins, larger than 11 000 daltons, were detected and their coding regions were mapped on the F plasmid genome. Three of them were assigned by taking into account the known nucleotide sequences (Murotsu et al. 1981; K. Yoshioka, personal communication). The coding directions of some proteins were determined by inserting the lac promotor into one of the recombinant plasmids and analyzing the increase in production of the proteins. The coding direction of the five proteins analyzed so far was uniform. Comparison of these results with a functional map of miniF suggested possible roles of the proteins.

Effect of nalidixic acid and novobiocin on pBR322 genetic expression in Escherichia coli minicells

The effects of two deoxyribonucleic acid (DNA) gyrase inhibitors, nalidixic acid and novobiocin, on the gene expression of plasmid pBR322 in Escherichia coli minicells were studied. Quantitative estimates of the synthesis of pBR322-coded polypeptides in novobiocin-treated minicells showed that the synthesis of a polypeptide of molecular weight of 34,000 (the tetracycline resistance protein) was reduced to 11 to 20% of control levels, whereas the amount of a polypeptide of 30,500 (the beta-lactamase precursor) was increased to as much as 200%. Nalidixic acid affected the synthesis of the tetracycline resistance protein similarly to novobiocin, although to a lesser extent. The effects of nalidixic acid were not observed in a nalidixic-resistant mutant; those induced by novobiocin were only partially suppressed in a novobiocin-resistant mutant. The synthesis of one of the inducible tetracycline-resistant proteins (34,000) coded by plasmid pSC101 was also reduced in nalidixic acid- and novobiocin-treated minicells. These results suggest that the gyrase inhibitors modified the interaction of ribonucleic acid polymerase with some promoters, either by decreasing the supercoiling density of plasmid DNA or by altering the association constant of the gyrase to specific DNA sites.

Functional analysis of hybrid plasmids carrying genes for lambda site-specific recombination

A number of hybrid plasmids, carrying lambda genes involved in site-specific integrative recombination, have been constructed in vitro. Analysis of protein synthesis in Escherichia coli minicells has shown that Int protein is synthesized only when int gene is expressed constitutively. The plasmids RSF2124::lambda-CD, RSF2124::lambda-Cint-c57, and pInt lambda were able to integrate into the chromosome of E.coli at the attB. The integration of hybrid plasmids into the genome of bacteria has also been shown for polA1 strains restricting the autonomous replication of ColE1 type plasmids. Genetic markers of hybrid plasmids are maintained in polA1 bacteria for at least 50 generations under nonselective conditions. The Southern blotting experiments using [32P]pBR322 DNA and EcoRI fragments of E. coli polA1 chromosome carrying integrated plasmid pInt lambda demonstrated that in this strain hybrid plasmids can be observed only when integrated into the attB of the chromosome according to Campbell's model of integration. In the cells, where autonomous replication of plasmids is possible, they can be observed both in extrachromosomal and integrated states. The integration of the ColE1 replication origin into the chromosome of bacteria is not lethal for the cells. Only attP and the int gene of lambda are necessary for the integration of hybrid plasmids under conditions of effective int gene expression. If the level of Int protein synthesis is high enough, the prophage excision can be observed in the absence of Xis product. The six-fold decrease of Int protein concentration in the cell (in case of pInt lambda 2 as compared to pInt lambda 1) is critical both for integration and excision.

Molecular cloning, correlation of genetic and restriction maps, and determination of the direction of transcription of gnd of Escherichia coli

Expression of the gene gnd of Escherichia coli, which encodes 6-phosphogluconate dehydrogenase, is regulated by growth rate. Using deoxyribonucleic acid from the specialized transducing phage lambda h80 dgnd his as the source of gnd, we cloned restriction fragments carrying the complete gene and portions of it on the plasmid vector pBR322. A hybrid plasmid carrying a 3.7-megadalton HindIII restriction fragment from the phage was prepared and found to be gnd+. Through restriction mapping of this fragment and subcloning segments of it, we prepared a gnd+ hybrid plasmid which carried only 1.85 megadaltons of E. coli deoxyribonucleic acid. A cleavage site for the restriction endonuclease PstI was located on the genetic map of gnd by cloning adjacent EcoRI-PstI restriction fragments and crossing the resulting hybrid plasmids with previously mapped gnd deletion and bacteriophage Mu insertion mutants. A maxicell experiment was used to determine the direction of transcription of gnd, to identify which EcoRI-PstI fragment contains the gnd promote, and to localize th beginning of the structural gene to a region about 850 +/- 150 base pairs from the PstI cleavage site. A fine-structure restriction map surrounding the PstI cleavage site was prepared for endonucleases KpnI, HincII, HaeIII, HpaII, and TaqI.