Genetic transformation in the methanogen Methanococcus voltae PS

Mutations causing requirements for histidine, purine, and vitamin B12 were obtained in strain PS of Methanococcus voltae (archaebacteria) upon irradiation with UV or gamma rays. The first two mutations were shown to revert at low frequencies and were used to demonstrate the occurrence of transformation with homologous, wild-type DNA. The transformation rates obtained for these presumably chromosomal markers were in the range of 2 to 100 transformants per microgram of DNA. Mutants resistant to 2-bromoethanesulfonate and to 5-methyl-DL-tryptophan were also isolated.

Immunity repressor of bacteriophage P2. Identification and DNA-binding activity

The product of gene C of the temperate bacteriophage P2, the immunity repressor, can be detected as a unique band eluting from phosphocellulose columns at 0.12 M-potassium phosphate when differentially labelled with a radioactive amino acid: the band is absent when phages that either have lost gene C through deletion or carry a suppressor-sensitive mutation in the gene are used. The repressor in its monomeric form is about 11,000 in molecular weight. At near physiological salt concentrations, the form predominantly recovered is the dimer. In filter-binding assays, the partially purified repressor binds wild-type P2 DNA strongly. It does not bind DNA of P2 vir94, a deletion that removes all the genetic elements involved in the regulation of lysogeny; it also does not bind, or binds inefficiently, DNA of P2 vir3, a mutation in the operator that controls the early replicative functions of P2. At the concentrations employed, the dimer is the active form in binding. The P2 repressor clearly differs in several features from the well-studied immunity repressor of bacteriophage lambda.

DNA fusion product of phage P2 with plasmid pBR322: a new phasmid

The chromosome of the temperate bacteriophage P2 and that of the plasmid pBR322 have been joined in vitro after treatment with restriction endonuclease EcoRI. The fusion product - a phasmid - can behave as a plasmid, as a phage and as a prophage. It can replicate its DNA under the control of either the specific replication mechanism of the parent phage in a polA mutant or that of the parent plasmid in a rep mutant. Several interesting interactions between the two replication modes are indicated. In particular, phage particles may be produced even when the phage mode of DNA replication is blocked, and this throws new light on the involvement of the early gene A in the regulation of late gene expression in phage P2.

[Remote results and critical review of the use of the Sparks-Mandril prosthesis]

Long-term clinical results and pathologic features, both macroscopic and microscopic, of 24 Sparks-Mandril grafts as femoro-popliteal substitutes are reviewed. High rate of complications and low percentage of patency are stressed. Further use of this graft is not recommended.

[Use of the human umbilical vein as a vascular prosthesis. Experimental study]

The possible use of the human umbelical vein as a vascular transplant, following appropriate chemico-physical treatment is discussed. The properties of this new prosthesis have been studied on the basis, first, of physical and dynamic tests and, thereafter, following experimental intervention on 12 dogs in which a segment of the abdominal aorta was replaced. The animals were angiographed at varying times from the operation, up to a maximum of 8 months, and finally sacrificed for thorough histological study using various techniques.

Recombination in bacteriophage P2: recA dependent enhancement by ultraviolet irradiation and by transfection with mixed DNA dimers

Bacteriophage P2 is known for its exceptionally low rate of spontaneous (non-integrative) recombination, which however may be stimulated by ultraviolet irradiation of the phage. We show here that ligated dimers, made in vitro from mixtures of DNAs of two P2 mutants, upon transfection of lysozyme-spheroplasts give origin to recombinants at high frequency. While spontaneous P2 recombination occurs independently of the main recombination pathway of the bacteria, P2 recombinant formation following either ultraviolet irradiation or transfection with DNA dimers requires at least some element of such a pathway, since it is absent or greatly reduced in recA- bacteria or spheroplasts. It would seen that, in the course of its lytic development, P2 deploys a mechanism that inhibits the main recombination pathway of the host cell, or assumes DNA configurations refractory to it.

Further physical characterization of deletion and substitution mutants affecting the control of lysogeny in bacteriophage P2

A deletion of phage P2, del6 (L.E. Bertani, 1980), thought to remove the structural gene int, and a deletion/substitution, vir94, thought to remove genes int, C and cox, were mapped by electron microscopy, using the heteroduplex technique. Four independent deletion/substitution mutations, all affecting the regulatory region of P2, were compared in all possible combinations with the same technique: two showed sequence homology in their substitution DNA. The results confirm the model proposed for the origin of these mutants, analogous to that for the origin of transducing variants in phage lambda, but suggest in first approximation that the exchange between the P2 DNA and the chromosome of the host bacterium may occur at several different bacterial sites. A map of the regulatory region of P2, based on all data available from the study of deletions and insertions, is presented.

Tandem pentuplication of a DNA segment in a derivative of bacteriophage P2: its use in the study of the mechanism of DNA annealing

From a tandem duplication mutant of phage P2, triplication, quadruplication and pentuplication forms were derived. They were recognized by decreased virion heat stability resulting from the increase in DNA content, and were confirmed by electron microscope heteroduplex mapping. These forms of partially repeated DNA are quite stable in P2 because of the low level of recombination typical of this phage. Under conditions normally employed for full DNA renaturation, these high order repeat chromosomes gave often incomplete renaturation over the repeated segments. Based on current models for DNA renaturation, several predictions were made and tested. The results, although not quantitatively exhaustive, indicated that base pairing proceeding from a nucleation site was sufficiently slow to allow a second nucleation to occur with a fair probability over a length of a few thousand base pairs.

Defective particle assembly in wild type P2 bacteriophage and its correction by the lg mutation

The mutation lg of phage P2 has been located on the genetic map of P2 to the right of, and closely linked to, the del2 deletion, probably within tail gene F. The lg mutation causes larger burst sizes, compared with the wild type, especially at high incubation temperatures. The frequency of defective particles is lower in preparations of P2 lg than in those of wild type P2. It seems that the mutation lg improves the efficiency of particle assembly.

Structure and position of a complex chromosomal aberration in bacteriophage P2

The P2 phage mutation vir56, like the previously studied vir22, is the result of an unequal replacement of a chromosome segment with non-homologous DNA. The end positions of the replacements are essentially the same in the two mutants, whereas the lengths of the replacements are quite different. A third chromosomal aberration, del3, has similar structure and position. These results strengthen the suggestion that the left ends of these three aberrations coincide with the point of exchange in integrative recombination.

Deletions in bacteriophage P2. Circularity of the genetic map and its orientation relative to the DNA denaturation map

Several types of viable chromosomal deletions of bacteriophage P2 were isolated. One type gives the immunity insensitive phenotype and may extend to the genes for the immunity repressor (C) and for integrative recombination (int). Two other types delete genes (old and fun) known to be active in the lysogenic state. For such deletion mutants the relationship between particle density and DNA length was established. The deletions were located in respect to previously mapped genes and the results were compared with electron microscopical studies (by Inman and collaborators) of the P2 chromosome. It is concluded that the best representation of the genetic map of P2 is circular. The cohesive ends of the linear P2 DNA molecule are most likely formed between genes old and Q. Except for the neighborhood of gene old, the previously published, linear genetic map of P2 (Lindahl) is colinear with the melting map of the P2 chromosome (Inman). Preliminary evidence for some specific recombination event often accompanying integrative recombination between phage chromosomes is presented.

Removal of unwanted proteins from cell extracts by means of antiserum

The efficiency of removal of soluble proteins in cell-free bacterial extracts by means of antiserum from rabbits immunized with similar extracts was measured. Precipitation followed by Sephadex gel-chromatography was used. Up to 80% (exceptionally 90%) removal could be obtained. The method might be applied to enrichment for "foreign" cell-extract components, for example, viral products in virus infected cells. Tests for the specificity of the method are also presented.

Constitutive expression of bacteriophage P2 early genes resulting from a tandem duplication

A tandem-duplication mutant of bacteriophage P2 was isolated. Physically, its particles are characterized by a higher buoyant density and lower heat stability than the wild type, both consequences of increased DNA content. Genetically, the mutant is easily recognized by its insensitivity to control by the immunity-specific repressor. The duplication covers part of gene B, necessary for phage DNA replication. To explain the immunity-insensitivity of the duplication it is proposed that the promoter, but not the operator site, in the early gene operon is duplicated in this mutant. By crosses with a gene-B mutant, a recombinant carrying a heterozygous duplication was isolated.

[Free aminoacids and cerebral lipids in the rat following porto-cava anastomosis]

Free aminoacids and cerebral lipids were studied in rats following porto-cava anastomosis with total deviation of the portal flow. No difference in lipid pattern with respect to the controls was noted after 1 month. Changes in free aminoacids, however, were observed, including a significant increase in gamma-aminobutyric acid (GABA) and a significant decrease in glutamic acid. The meaning of these results with respect to the pathogenesis of porto-cava encephalopathy is discussed.