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R D Porter

Publications and source records attributed to R D Porter.

6 recordsLinked to original sources
PubMed1979

Bacteriophage-associated gene transfer in pneumococcus: transduction or pseudotransduction?

Lysates of pneumococcal phage PG24 transferred genes from one host to another in a process with many of the properties of generalized transduction, in that the host genes were packaged in DNase-resistant particles that closely resembled infectious phage in physical properties, adsorbed to the recipient cells like phage, and were inhibited by antisera to the phage and by trypsin. However, phage processes did not complete the transfer of host DNA as they did phage DNA. Instead, gene transfer required development of competence and entry of the host DNA by the endonuclease-dependent pathway used for transforming and transfecting DNA. This process often occurred on the assay plate hours after adsorption of the particles to the cells, and the transfer was DNase sensitive if challenged at this time. Phenotypic expression was therefore also delayed. The product of entry was like that in transformation, a single strand of DNA that integrates by formation of a hex-sensitive donor-recipient heteroduplex. Whether this gene transfer process is unique to this system or is only the first one described is not clear. The term "pseudotransduction" may be useful in calling attention to its unexpected features. The DNA of PG24 phage has anomalous physical properties reflecting unusual bases.

Bacteriophages↗
PubMed1978

Transfection in pneumococcus: single-strand intermediates in the formation of infective centers.

Transfection has been found and characterized in pneumococcus. For replicating omega3 phage DNA extracted from infected cells, transfection was relatively efficient and rose linearly with DNA concentration and quadratically with time, according to T(T - 3.5) min(2). For mature DNA extracted from phage particles, transfection was hardly detectable below 1 mug/ml but increased about as the cube of the DNA concentration up to 100 mug/ml, and was still rising at concentrations over 200 mug/ml. The kinetics suggest a dependence on a mixed cubic function of the time of exposure of cells to mature DNA. Cell and phage DNAs competed with each other for transformation and transfection. Transfection was reduced much more strongly than transformation in cells that were deficient in the membrane-bound endonuclease required for conversion of donor duplex DNA to intracellular single strands; these data agree with the kinetic data in implying that independent entry of segments of two strands is necessary for transfection by replicating omega3 phage DNA and entry of at least three strands is necessary for transfection by mature DNA. To reconcile differing DNA concentration dependences of transfection and transformation with a common entry path, it was necessary to reexamine data on transformation and to recognize that this process continued to rise slowly through the concentration region usually described as "plateau." These results and the transfection data reflect multiple binding and nicking events that occurred on the cell surface before entry. Our conclusion is that transfection in pneumococcus occurs by association inside the cell of segments of single strands of phage DNA that have entered independently, creating gapped structures that need repair synthesis to create infective centers. Physical recombination is therefore automatically a prerequisite to transfection.

Bacteriophages↗
PubMed1976

Characterization of some pneumococcal bacteriophages.

The growth of pneumococcal phages at high cell and phage densities is enhanced strongly by the substitution of potassium for sodium in the medium. Initial titers of 2 X 10(10) to 4 X 10(10) PFU/ml are readily obtained, and concentrated stocks are stable in a storage buffer described here. The mechanism of the cation effect is obscure. Phages omega3 and omega8 each have linear double-stranded DNA of 33 X 10(6) daltons per particle, with an apparent guanine plus cytosine content of 47 to 49 mol%, as determined by buoyancy and melting temperature, but with an unusual absorbance spectrum. Efficiency of plating is high if sufficient time is allowed for a relatively slow adsorption, which differs several-fold in rate between the two phages. Morphologically, these and other pneumococcal phages are similar to coliphage lambda but with a longer tail and tail fiber. Upon UV inactivation, omega3 and omega8 have D37 values of 33 and 55 J/m2, respectively, and each shows multiplicity reactivation. A total of 13 ts mutants have been isolated from the two phages, representing only two complementation groups; complementation and recombination occur between omega3 and omega8 mutants. Both phages provoke high-titer antisera with extensive cross-reactivity against a number of newly isolated pneumococcal phages.

Adsorption↗
PubMed1975

Secretory activity and aryl acid content of serum, urine, and cerebrospinal fluid in normal and uremic man.

Serum from uremic human subjects causes net fluid secretion in proximal straight tubules isolated from rabbit kidneys in a manner similar to paraaminohippuric acid. In the present study, we determined the relation between the concentration of aryl acids (hippuric acid, benzoic acid, etc.) In serum, urine, and cerebrospinal fluid (CSF) and the capacity of the biologic fluids to cause fluid secretion in renal tubules. The concentration of aryl acids in serum and urine as estimated by fluorometric assay (Fl-Hipp) was related to the secretory activity (SA) estimated by bioassay in a direct linear fashion over a 10,000-fold range of concentrations. Fl-Hipp and SA were strikingly elevated in the serum of uremic patients. Hippuric acid determined by gas-liquid chromatography accounted for approximately one-fourth of the secretory activity of serum and urine; benzoic acid was present only in trace amounts; the remainder of the secretory activity of uremic serum is probably due to derivatives of aryl acids which are detected as Fl-Hipp. The relation between creatinine clearance and the SA or Fl-Hipp concentration of serum was hyperbolic; both the SA and Fl-Hipp content of serum increased sharply when creatinine clearance fell below 10 ml. per minute. The SA and Fl-Hipp content of CSF was increased in uremic patients; however, the serum content exceeded that of the CSF by more than fourfold suggesting an exclusion mechanism for aryl acids in the central nervous system. We conclude that the secretory activity of uremic serum is due to the accumulation of aryl acids, probably of the hippurate class, and, further, that relatively high levels of these biologically active substances may contribute to general organ dysfunction in uremia owing to their potential to act as competitive inhibitors of organic anion transport.

Animals↗