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B Hohn

Publications and source records attributed to B Hohn.

At least 91 records · Page 5Linked to original sources
PubMed1984

Selective isolation of cosmid clones by homologous recombination in Escherichia coli.

A procedure for selection of specific cosmid clones by homologous recombination between cosmid clones from a library and sequences cloned into a plasmid has been developed. Cosmid libraries constructed in a rec- host strain are packaged in vivo into lambda particles. Appropriate aliquots are then introduced into a rec+ host containing the sequence used for selection cloned into a plasmid vector without sequence homology to the cosmid vector. After a short time for recombination, the cosmids are packaged in vivo. Cosmids that have taken up the plasmid by homologous recombination are isolated by plating under conditions selecting for the antibiotic resistance markers carried by both vectors. The recombined cosmids can lose the inserted sequence by another homologous recombination event and, after packaging in vivo, these revertants can be identified on appropriate indicator plates.

Animals↗
PubMed1983

DNA sequences necessary for packaging of bacteriophage lambda DNA.

The extent of DNA flanking the "cohered cohesive end" site of bacteriophage lambda DNA, which is required for packaging, was determined by using defined DNA fragments and a cosmid in vivo packaging assay. From the right end of lambda DNA a 20- to 36-base-pair stretch extending from the center of the cohered cohesive ends is shown to be required, whereas the packaging efficiency of cosmids extending to 70 base pairs into the left lambda arm is reduced to 10% (compared to a fragment extending until about 80 base pairs). A 60-base-pair stretch of the left arm leaves an efficiency of only 1%. The segment thus delineated, by the nature of the assay, is both necessary and sufficient for the binding of packaging proteins to the DNA, the packaging of DNA itself, the DNA cleavage, and successful injection of the DNA into a bacterial host. By contrast, in vitro packaging of restriction fragments of mature lambda DNA directly demonstrated the selectivity of the packaging proteins for the fragment originating from the left end of the DNA. The results of the two complementary experiments are discussed in terms of the various steps before, during, and after packaging for which different sequences flanking and including the cohered cohesive ends might be required.

Bacteriophage lambda↗
PubMed1983

[Rheumatoid arthritis, obliterating bronchiolitis and D-penicillamine. Apropos of a new case with ultrastructural examination and review of the literature].

Over recent years, several cases have been reported of bronchiolitis obliterans, of very rapid onset and serious clinical course in patients with rheumatoid arthritis being treated with D-Penicillamine. After reporting a new case, the authors stress the unusual features of this bronchiolar condition which is probably of iatrogenic origin and irreversible, with death occurring within a few years. The pathogenesis is poorly understood and many questions still remain concerning the relationships between rheumatoid arthritis, the bronchiolar lesions and D-Penicillamine in this disease of pulmonary collagen. The ultrastructural examination and the morphometric examination of this new case suggest the presence of predominantly type III collagen, which is normally present in the lungs in only small quantities.

Arthritis, Rheumatoid↗
PubMed1982

[Legionnaires' disease with digestive tract lesions. One case].

In the case reported pulmonary Legionella infection was diagnosed by sputum cultures even though immunofluorescence tests were negative. The patient had positive Coomb's test due to circulating auto-antibodies which disappeared after he recovered. The course of the disease was prolonged by perforation of the coecum requiring excision of the colon and terminal ileostomy. Erythromycin had to be given intravenously. Pathological examination of the digestive tract lesions showed inflammatory colitis with presence of Legionella pneumophilia which seemed to have been responsible for the complication. This is the first time a digestive lesion caused by this organism is described, adding yet another extrapulmonary visceral involvement to those already reported and suggesting that Legionella may spread throughout the body.

Autoantibodies↗
PubMed1982

In vivo recombination of cauliflower mosaic virus DNA.

LIGATION AND RECOMBINATION OF THE DNA OF CAULIFLOWER MOSAIC VIRUS (CAMV) IS DEMONSTRATED BY THE FOLLOWING EXPERIMENTS: (i) Ligation: Different noninfectious fragments of the CaMV genome (obtained after insertion into plasmid pBR322 followed by enzymatic excision) regained infectivity when mixtures of them were used to inoculate their host. The symptom appearance was delayed by comparison with a typical CaMV infection, and only the newly formed leaves were affected. (ii) Recombination: Pairs of noninfectious recombinant full-length CaMV genomes (integrated into pBR322 at different restriction endonuclease sites) regained infectivity upon simultaneous inoculation of a sensitive host. The symptomatology of the resulting infection was indistinguishable from that of a typical CaMV infection. We show that progeny DNA had the same characteristics (size, structure, restriction endonuclease digestion pattern) as bona fide CaMV DNA, and that the vector pBR322 had been completely eliminated. A cloned tandem dimer of CaMV DNA with a partial deletion similarly was infectious in the plant assays. This system should be useful to study the expression of mutant genomes, thus allowing characterization of the CaMV genes.

Journal Article↗
PubMed1981

Plasmid vectors for positive selection of DNA inserts controlled by the lambda pL promoter, repressor and antitermination function.

Hybrid plasmids consisting of pBR322 or pOP203-3 and the EcoRI-D fragment of lambda DNA kill their bacterial host upon expression of a lambda gene (probably the kil function) located either between or across the SalI sites. The plasmids from surviving hosts are acquired deletions that remove the lambda kil gene or insertions that block the transcription of the kil gene. Some plasmids probably carry point mutations. Based on these findings, we constructed two vector plasmids, pKL1 and pHA10, which can be used for a direct positive selection of cloned fragments. These plasmids are particularly useful for the cloning and selection of N-unresponsive termination signals using BamHI and its isoschizomers. The DNA fragments cloned into these plasmids are under control of the strong pL promoter, which can be regulated by the lambda repressor, and the antitermination activity of the N gene product.

Bacteriophage lambda↗
PubMed1980

Infectivities of native and cloned DNA of cauliflower mosaic virus.

Infectivity assays on turnips reveal that (i) cauliflower mosaic virus (CaMV) DNA, whether circular or linear, is as infectious as the complete virus; (ii) linear DNA obtained with restriction enzymes from the native CaMV DNA has the same specific infectivity as when first cloned in plasmid (pBR322) or bacteriophage (lambda gtWES) vectors and then restricted at the cloning site; (iii) in all cases studied mosaic symptoms are accompanied by virus production. DNA isolated from these viruses is again circular and possesses the three "gaps" characteristic of CaMV DNA. The cloned CaMV DNA, when linked to the vector DNA, is noninfectious or exhibits very low infectivity.

Cloning, Molecular↗
PubMed1980

A small cosmid for efficient cloning of large DNA fragments.

The production and use of the 6 kb cosmid pHC79, a derivative of pBR322, is described. It can be used for cloning of fragments cleaved by EcoRI, ClaI, BamHI (also BglII, BclI, Sau3A and MboI), SalI (also XhoI and AvaI), EcaI and PstI. Hybrid cosmids containing inserts in the size range of 40 kb are packaged in vitro and transduced with an efficiency of 5 X 10(4) - 5 X 10(5) clones/microgram of insert DNA. Prefractionation of the DNA fragments to be cloned into 40 kb sized fragments ensures the cloning of contiguous stretches of DNA. Proteins produced in vitro by the cosmid pHC79 are identical to the ones produced by its pBR322 parent.

Bacteriophage lambda↗
PubMed1980

Restriction map of native and cloned cauliflower mosaic virus DNA.

Cloned CaMV DNA replicates faithfully in Escherichia coli, since the restriction map of the cloned DNA can be superimposed over that of the native viral DNA. However, some short fragments were difficult to detect in the restricted native viral DNA, whereas they formed clear bands when derived from cauliflower mosaic virus (CaMV) DNA clones propagated in the E. coli host. Apparently, the small fragments that carry variable-length single-stranded gaps present only in native viral DNA, give rise to diffuse weak bands difficult to recognize in gels. Comparison of maps for several CaMV strains permits evaluation of their possible evolutionary relationship.

Chromosome Mapping↗
PubMed1978

Identification of a host protein necessary for bacteriophage morphogenesis (the groE gene product).

Mutations in the groE gene of Escherichia coli, which block the correct assembly of the phage lambda head, have been previously described. Many groE mutations exert pleiotropic effects, such as inability to propagate phages T4 and T5 and inability to form colonies at 43 degrees. With the help of the EcoRI and HindIII restrictionenzymes and the appropriate phage vectors, we have constructed two lambda transducing phages, called W3 and H18, that carry the groE+ bacterial gene. Upon lysogenization by phage H18 the groE bacterial mutants recover their gro+ phenotype for both phage growth and the ability to form colonies at 43 degrees. We have identified the groE+ bacterial gene product as a protein of 65,000 molecular weight. Mutants of the W3 transducing phage that were selected on the basis of their ability to propagate on some groE mutant hosts induce the synthesis of a groE protein with altered electrophoretic mobility.

Bacterial Proteins↗
PubMed1978

DNA clones containing mouse immunoglobulin kappa chain genes isolated by in vitro packaging into phage lambda coats.

Endonuclease EcoRI-digested DNAs from BALB/c mouse embryos and MOPC 321 (a kappa chain secretor) myeloma were fractionated by agarose gel electrophoresis, and the DNA fragments containing part or all of the MOPC 321 kappa chain structural gene sequences were visualized by the Southern gel blotting technique using as the hybridization probes pCRI plasmids containing all or part of the enzymatically synthesized cDNA transcripts of the MOPC 321 kappa chain mRNA. The clear differences observed in the hybridization patterns of the two DNAs are in agreement with our previously reported results obtained with endonuclease BamHI and confirms that the sequence arrangement of kappa chain genes is different in the embryo and myeloma cells. We have cloned most of the kappa-sequence-positive EcoRI DNA fragments in Charon 4A phage by using the highly efficient in vitro phage lambda DNA packaging method, and we have characterized the cloned mouse DNA sequences by agarose gel blotting and R-loop mapping in electron microscopy. These studies identified, among others, one EcoRI DNA fragment which contains both variable and constant immunoglobulin kappa-gene sequences and is present only in the myeloma DNA. The two sequences are separated by a 2.8-kbase intron. We tentatively conclude that the kappa gene sequences on this DNA fragment underwent somatic rearrangement.

Animals↗
PubMed1978

Cosmids: a type of plasmid gene-cloning vector that is packageable in vitro in bacteriophage lambda heads.

Evidence is presented that ColE1 hybrid plasmids carrying the cohesive-end site (cos) of lambda can be used as gene cloning vectors in conjunction with the lambda in vitro packaging system of Hohn and Murray [(1977) Proc. Natl. Acad. Sci. USA 74, 3259--3263]. Due to the requirement for a large DNA molecule for efficient packaging, there is a direct selection for hybrids carrying large sections of foreign DNA. The small vector plasmids do not contribute a large background in the transduced population, which is therefore markedly enriched for large hybrid plasmids (over 90%). The efficiency of the in vitro packaging system is on the order of 10(5) hybrid clones per microgram of foreign DNA for hybrids in the 20--30 million dalton range.

Coliphages↗
PubMed1977

Packaging recombinant DNA molecules into bacteriophage particles in vitro.

Recombinant phage genomes made in reactions with purified enzymes may be recovered directly by packaging into phage heads in vitro. The process is efficient and nonselective and offers containment in initial stages of handling recombinant DNA. Ligase [poly(deoxyribonucleotide):poly-(deoxyribonucleotide) ligase (AMP-forming), EC 6.5.1.1] reaction products can recombine with endogenous phage DNA during packaging, but UV-irradiation eliminates the biological activity of the endogenous DNA.

Coliphages↗
PubMed1976

Capsid transformation during packaging of bacteriophage lambdaDNA.

Assembly pathways of complex viruses might not be simple additions of one protein after another with rigid tertiary structure. It might in fact involve shifts in subunit structure, movement of subunits relative to each other to form new arrangements, transient action of proteins and protein segments, involvement of structure forming 'microenvironments' of the host. Thus morphogenesis of the bacteriophage lambda head starts with the formation of a core-containing DNA-free petit lambda particle. In a first transition, and dependent on a host function, the core is released, minor protein components of the capsid are processed and the particle's structure is altered, as shown by a change of its hydrodynamic properties. The resulting 'prehead' undergoes a second transition triggered by a complex of DNA and recognition protein (A-protein). This transition is more drastic than the first one. The particle doubles its volume without increasing in protein mass, the shell becomes thinner, and the surface structure is changed. Concomitantly with this process, the DNA becomes packaged and the particle becomes able to bind the small 'D-protein' in amounts equimolar to the capsid protein, which it could not do before. The D-protein addition probably causes another shift of the capsid structure. DNA packaging is completed, and the DNA is cut from concatemeric precursors to unit length molecules. Binding sites are created for the tail connector molecules which in turn allow the independently assembled tail to attach. Research on these processes proceeds along several lines: comparison of physical and chemical properties of particles accumulating in mutants; pulse-chase experiments on assembly precursors; morphogenesis in vitro; and model transitions of aberrant lambda polyheads.

Capsid↗