"Pop-off" technic. The ultrastructure of paraffin-embedded sections

Stained paraffin embedded sections sometimes contain a precise area that warrants further investigation at an ultrastructural level. A technic is described whereby an area in question may be reembedded into plastic and sectioned for examination under the electron microscope. The decoverslipped paraffin section is "popped-off" into an inverted BEEM capsule. Suspected viral inclusions in sections may be identified or ruled out with this technic. Special stains, especially heavy metal applications, not able to be utilized in conventional plastic embedding may be reembedded into plastic. The metallic granules may be visualized ultrastructurally without further grid staining. This method is especially helpful for cell smears and cell monolayers since they may be the only material available for study. Although ultrastructural detail is often poor, one does have the ability to study the identical section under both the light and the electron microscopes.

Contacts between DNA gyrase and its binding site on DNA: features of symmetry and asymmetry revealed by protection from nucleases

DNA gyrase supercoils DNA by passing one DNA segment through another by means of a reversible double-strand break at specific DNA sites. We determined the nucleotide sequence of two highly preferred gyrase binding sites and analyzed the grip of gyrase on the DNA by using protection from nuclease attack. The DNA-breakage site of gyrase was centered in about 50 base pairs (bp) of DNA that was completely protected from DNase I and flanked by DNA regions cut at average intervals of 9.9 bases. The same pattern of protection from DNase I was observed with topoisomerase II', an enzyme that shares structural homology with gyrase. The gyrase site of DNA breakage was off-center in the 140 bp of DNA protected from exonuclease III digestion. ATP or inhibitors of gyrase had little specific effect on DNase I protection. On addition of a nonhydrolyzable analogue of ATP, previously stable barriers to exonuclease III were invaded and new barriers appeared. We discuss a detailed model uniting these results with previous data on gyrase structure and mechanism.

Changes in the synthesis of ribosomal ribonucleic acid and of poly(A)-containing ribonucleic acid during the differentiation of intestinal epithelial cells in the rat and in the chick

Epithelial cells were isolated from rat and chick small intestine by techniques which separated subpopulations of differentiating villus and upper crypt cells from each other and from populations of mitotically dividing lower crypt cells. Incorporation of precursors into epithelial-cell DNA, cytoplasmic rRNA and cytoplasmic poly(A)-containing RNA occurred in the lower crypt cells in vivo when precursor was supplied from the vascular system of the intestine. Incorporation of precursor into 28S and 18S rRNA continued in the upper crypt cells, but occurred to only a very slight extent (if at all) in villus cells, whereas incorporation into poly(A)-containing RNA continued (at a diminishing rate) as the differentiating cells migrated along the villi. When precursor was supplied from the intestinal lumen, its incorporation into DNA and into rRNA of crypt cells was not very different from that observed with the other mode of precursor administration, but incorporation into villus-cell poly(A)-containing RNA then occurred at essentially the same rate in all intestinal epithelial cells in vivo. Cytoplasmic poly(A)-containing RNA appeared to turn over in rat crypt cells with a half-life not exceeding 24 h; crypt-cell rRNA showed no turnover and no evidence could be found for the presence of 'metabolic DNA'.

Poly(adenosine diphosphate ribose) synthetase activity in nuclei of dividing and of non-dividing but differentiating intestinal epithelial cells

Poly(ADP-ribose) synthetase activity is found in nuclei of regenerating epithelial cells in the lower half of the crypts of guinea-pig small intestine. Nuclei from non-dividing but differentiating and maturing cells in the upper crypts and on the villi contain no more than about 10% of the synthetase activity of lower-crypt cell nuclei. The product in the active nuclei is shown to be 80% poly(ADP-ribosylated) protein and 20% mono(ADP-ribosylated) protein; 60% of thetotal labelled product was attached to acid-soluble proteins (including histones), and 40% to acid-insoluble (non-histone) proteins. The average number of ADP-ribosyl units in the oligomeric chains of the poly(ADP-ribosylated) proteins was 15 but the range of sizes of (ADP-ribose) oligomers attached to nuclear proteins was smaller in villus than in crypt cell nuclei.

Site-specific cleavage of DNA by E. coli DNA gyrase

E. coli DNA gyrase, which catalyzes the supercoiling of DNA, cleaves DNA site-specifically when oxolinic acid and sodium dodecylsulfate are added to the reaction. We studied the structure of the gyrasecleaved DNA because of its implications for the reaction mechanism and biological role of gyrase. Gyrase made a staggered cut, creating DNA termini with a free 3' hydroxyl and a 5' extension that provided a template primer for DNA polymerase. The cleaved DNA was resistant to labeling with T4 polynucleotide kinase even after treatment with proteinase K. Thus the denatured enzyme that remains attached to cleaved DNA is covalently bonded to both 5' terminal extensions. The 5' extensions of many gyrase cleavage fragments from phi X174, SV40 and Col E1 DNA were partially sequenced using repair with E. coli DNA polymerase I. No unique sequence existed within the cohesive ends, but G was the predominant first base incorporated by DNA polymerase I. The cohesive and sequences of four gyrase sites were determined, and they demonstrated a four base 5' extension. The dinucleotide TG, straddling the gyrase cut on one DNA strand, provided the only common bases within a 100 bp region surrounding the cleavage sites. Analysis of other cleavage fragments showed that cutting between a TG doublet is common to most, or all, gyrase cleavages. Other bases common to some of the sequenced sites were clustered nonrandomly around the TG doublet, and may be variable components of the cleavage sequence. This diverse recognition sequence with common elements is a pattern shared with several other specific nucleic acid-protein interactions.

The "Newsletter": a catalyst for learning in group psychotherapy

This article reports on an experiment in which members of a therapy group were invited to take turns doing process recordings of meetings, which were then circulated weekly to all members. The history of this "Newsletter," its benefits, the therapeutic goals, and the resistance it encountered are described. The method is seen as a potentially enriching tool for group psychotherapy.

Adenylate cyclase of human parathyroid gland

Experiments were performed on a particulate fraction from human parathyroid glands. A high activity of adenylate cyclase was detected which was linear with time and protein concentration. The enzyme had an optimum pH in the range of 7-8 and a Km for ATP of 0.44 X 10(-3) M. Ca++ had a profound inhibitory effect; a concentration of 0.5 mM Ca++ reduced enzyme activity by 60%. Maximal enzyme activity was obtained with 5 mM Mg++; higher concentrations of this cation also inhibited enzyme activity. The effect of Mn++ was similar to that of Mg++. Enzyme activity was stimulated by NaF, catecholamines, glucagon, and calcitonin. The effect of catecholamines seems to be mediated through beta-adrenergic receptors.

Exaggerated prostaglandin biosynthesis and its influence on renal resistance in the isolated hydronephrotic rabbit kidney

Basal and hormone-stimulated prostaglandin biosynthesis was compared in isolated perfused rabbit kidneys with and without ureteral obstruction. At 72 h there was enhanced responsiveness to bradykinin in the ureter-obstructed hydronephrotic kidney. The amount of prostaglandin-like substance released from the perfused kidneys by 25 ng of bradykinin was 533+/-163 ng from the ureter-obstructed, 28+/-4 ng from the contralateral, and 26+/-3 ng from the normal kidney. The enhanced response was also noted with angiotensin II and with norepinephrine. This exaggerated responsiveness by the ureter-obstructed kidney could not be explained by decreased prostaglandin (PG) destruction or by decreased renal peptide inactivation (bradykinin or angiotensin). There was no enhanced PG biosynthesis with exogenous arachidonate, suggesting there was no increase in cyclo-oxygenase activity in the ureter-obstructed kidney. Renal tubular transport of PG from medulla to cortex was apparently not essential for the enhanced PG biosynthesis to hormone stimulation since the same exaggerated responses were noted during perfusion with the ureter ligated. The cyclo-oxygenase inhibitor, indomethacin, increased basal perfusion pressure in the obstructed kidney and enhanced the magnitude and duration of the renal vasoconstriction produced by angiotensin II in the hydronephrotic kidney. These results suggest that the local exaggerated biosynthesis of PG may be occurring in the cortical resistance vessels and may be important to the alteration in blood flow and excretory function that occur in ureteral obstruction.

Inhibitory effects of hypermagnesemia on the renal action of parathyroid hormone

Available evidence indicates that serum magnesium (Mg++) levels influence the secretion rate of parathyroid hormone (PTH). Whether serum Mg++ concentrations also modify the action of PTH on its target organs has not been definitively established. The present experiments were designed to study this possibility. The effect of infusing PTH on the urinary excretion of cyclic AMP (cAMP) and PO4= was examined in five normal dogs at two different levels of serum Mg++. At normal serum Mg++ concentrations (1.89 +/- 0.14 mg/100 ml), PTH infusion increased cAMP excretion from 1.76 +/- 0.27 to 4.87 +/- 1.00 nmol/min and fractional PO4= excretion (FEPO4) from 1.58 +/- 0.36% to 23.1 +/- 2.17%. When an identical amount of PTH was given to the same dogs at a serum Mg++ of 4.36 +/- 0.20 mg/100 ml, FEPO4 increased to only 6.02+/-1.89% and cAMP from 1.31 +/- 0.23 to 1.89 +/- 0.39 nmol/min. Identical results were obtained in thyroparathyroidectomized hypermagnesemic dogs. Increased serum Mg++ levels had no effect on the phosphaturia produced by the infusion of dibutyryl cAMP to thyroparathyroidectomized dogs. In vitro studies using rat renal cortical slices revealed a progressive decrease in cAMP production in response to PTH as the Mg++ concentrations were increased in the incubation medium. The overall results indicate that hypermagnesemia inhibits the phosphaturic response to PTH by decreasing the renal production of cAMP. Plasma magnesium, therefore, may participate in a double feedback mechanism, not only controlling the release of PTH, but also altering the biological activity of the hormone at the level of the target organ.

The behaviour of oligodeoxynucleotides on thin-layer chromatography on polyethyleneimine-cellulose and ion-exchange paper electrophoresis. Applications in fractionating and sequencing terminally labelled oligodeoxynucleotides

The electrophoretic behaviour of oligodeoxynucleotides on ion-exchange papers was studied systematically with particular attention to applications in sequence analysis. Complex mixtures of larger oligonucleotides were fractionated by electrophoresis on cellulose acetate followed by t.l.c. on polyethyleneimine-cellulose. The behaviour of the oligonucleotides on polyethyleneimine-cellulose and on the two-dimensional system can provide a useful guide to their sequence. Detailed results from some of these experiments have been deposited as Supplementary Publication SUP 50031 (13 pages) at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1973), 131, 5.