Specific hybridization probes demonstrate fewer xenotropic than mink cell focus-forming murine leukemia virus env-related sequences in DNAs from inbred laboratory mice.

We have derived hybridization probes from analogous 100-base-pair segments located within the N-terminal region of gp70 coding sequences which differentiate xenotropic from mink cell focus-forming (MCF)-related murine leukemia virus (MuLV) DNAs. The MCF probe annealed to the integrated proviruses of all six MCF MuLV isolates tested; the xenotropic probe hybridized to the DNAs of all four xenotropic proviral isolates examined. No cross-hybridization was observed, and neither probe reacted with the env segments of amphotropic or ecotropic MuLV DNAs. Southern blot analysis of HindIII- or EcoRI-digested genomic DNAs from a variety of inbred laboratory mice demonstrated the presence of more MCF- than xenotropic MuLV-related segments in every strain tested.     

Nitrification and organic nitrogen formation in soils

Summary The formation of mineral nitrogen species and of organic nitrogen was studied in three different types of soils in relation to the application of the nitrification inhibitor nitrapyrin. The results indicate that nitrification brings about a deficit in total mineral nitrogen and a concomitant surplus in non biomass organic nitrogen. This phenomenon increases with increasing levels of applied ammonium nitrogen and soil organic matter. The phenomenon is considered to be due to the reaction of the transient nitrite formed with soil phenolic compounds and appears to be of significance in all soils in which nitrification occurs, even neutral to alkaline and low carbon soils.     

Regulation of luteal cell 3-hydroxy-3-methylglutaryl coenzyme A reductase activity by estradiol

Recent studies have suggested that estradiol or androgen precursor may stimulate steroidogenesis in the luteal cell by modulating intracellular sterol availability and metabolism. This investigation was performed to examine the effect of estradiol on de novo synthesis of cholesterol. Pregnant rats hypophysectomized and hysterectomized on Day 12 were treated for 72 h with either estradiol or testosterone. De novo cholesterol synthesis was determined by measurement of the specific activity of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, the rate limiting enzyme in cholesterol biosynthesis, in microsome-enriched preparations of luteal tissue and incorporation of [14C] acetate into cholesterol by corpora lutea incubated in vitro. Estradiol or testosterone treatment caused a 4- to 5-fold stimulation of luteal cholesterol biosynthesis, as measured by these techniques. NaF, an inhibitor of phosphatase which blocks the conversion of the inactive enzyme to the active form, reduced the HMG CoA reductase activity to 30% in corpora lutea obtained from either steroid or vehicle-treated rats. However, an increase in enzyme activity of comparable magnitude by steroids was observed whether microsomes were isolated with or without NaF. The effect of estradiol appears to be enzyme-specific, since it failed to affect the microsomal marker, NADPH-cytochrome c reductase. Since the cholesteryl ester content of corpora lutea falls in response to steroid treatment, rats were treated with 4-aminopyrazolo-[3,4d]pyrimidine (4-APP) to deplete cellular cholesterol content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of toxin biosynthesis by plasmids in Vibrio cholerae

Vibrio cholerae strain 569B Inaba harbouring P plasmid produced less toxin than the parent strain. To examine the effect of plasmid loss on toxin production, temperature-sensitive (ts) mutants of P, unable to replicate at 42 degrees C, were isolated. One ts plasmid was unstable at 42 degrees C and its loss yielded a cured strain that resumed a normal level of toxin biosynthesis characteristic of the plasmid-free parent strain. Toxin production was again suppressed in the cured strain after reacquisition of P plasmid. This suggested a role for plasmid-borne genes in the regulation of toxin biosynthesis. A mutant of strain 569B Inaba that produced mutant toxin was isolated by transfer of P and V plasmids. The mutant toxin was similar to choleragenoid because it did not give rise to symptoms of cholera but induced antitoxin immunity in rabbits.     

Caffeine tolerance: behavioral, electrophysiological and neurochemical evidence

The development of tolerance to the stimulatory action of caffeine upon mesencephalic reticular neurons and upon spontaneous locomotor activity was evaluated in rats after two weeks of chronic exposure to low doses of caffeine (5-10 mg/kg/day via their drinking water). These doses are achievable through dietary intake of caffeine-containing beverages in man. Concomitant measurement of [3H]-CHA binding in the mesencephalic reticular formation was also carried out in order to explore the neurochemical basis of the development of tolerance. Caffeine, 2.5 mg/kg i.v., markedly increased the firing rate of reticular neurons in caffeine naive rats but failed to modify the neuronal activity in a group exposed chronically to low doses of caffeine. In addition, in spontaneous locomotor activity studies, our data show a distinct shift to the right of the caffeine dose-response curve in caffeine pretreated rats. These results clearly indicate that tolerance develops to the stimulatory action of caffeine upon the reticular formation at the single neuronal activity level as well as upon spontaneous locomotor activity. Furthermore, in chronically caffeine exposed rats, an increase in the number of binding sites for [3H]-CHA was observed in reticular formation membranes without any change in receptor affinity. We propose, therefore, that up-regulation of adenosine receptors may underlie the development of tolerance to the CNS effects of caffeine.     

Effect of Light and Benzyladenine on Dark-Treated Growing Rice (Oryza sativa) Leaves II. Changes in Peroxidase Activity

Changes in peroxidase activity were studied in the attachedfirst leaf of dark-treated Oryza sativa L. cv. Bala seedlingsin response to benzyladenine and light treatments during laterperiods of leaf growth, prior to maturation. Darkness causeda mild decrease in peroxidase activity; but in illuminated leaves,the enzyme activity was stable at all times. There was a sharprise in peroxidase activity in dark-treated leaves upon lightor benzyladenine application, irrespective of the time of treatment.Benzyladenine treatment to illuminated leaves also caused arise in peroxidase activity. Exogenous hydrogen peroxide, glycolateand amizol resulted in a rise in peroxidase activity, whichwas further enhanced by benzyladenine treatment in both lightand dark incubated leaves. Proline maintained chlorophyll levels,whereas hydroxyproline caused chlorophyll degradation. Benzyladenineenhanced the proline effect and counteracted the hydroxyprolineeffect on chlorophyll. Both proline and hydroxyproline increasedperoxidase activity in the leaves of light and dark incubatedseedlings, and the enzyme activity further increased after benzyladeninetreatment. (Received December 7, 1984; Accepted May 8, 1985)     

Dual action of respiratory inhibitors: inhibition of germination and prevention of dormancy induction in lettuce seeds

`Grand Rapids' lettuce Lactuca sativa L. seeds germinate readily at 15°C but poorly at 25°C in darkness. When held in dark at 25°C for an extended period, the ungerminated seeds become dormant as shown by their inability to germinate or transfer to 15°C in darkness. Induction of dormancy at 25°C was prevented by exposure to CN<sup>−</sup>, azide, salicylhydroxamic acid (SHAM), dinitrophenol, and pure N<sub>2</sub> as determined by subsequent germination at 15°C on removal of inhibitors. The effectiveness of inhibitors to break dormancy declined as dormancy intensified. At relatively low levels, CN<sup>−</sup>, SHAM, and azide promoted dark germination at 25°C while at high levels they were inhibitory. Uptake of O<sub>2</sub> by seeds held at 25°C for 4 days in 1.0 millimolar KCN was inhibited by 67% but was promoted 61% when KCN was removed. Correspondingly greater inhibition (79%) and promotion (148%) occurred when 1.0 millimolar SHAM was added to KCN solution. When applied alone, SHAM had little effect on O<sub>2</sub> uptake. These data indicate that Cyt pathway of respiration plays a dominant role in the control of both dormancy induction and germination of lettuce seeds, and `alternative pathway' is effectively engaged in presence of CN⁻. The channeling of respiratory energy use for processes governing germination or dormancy is subject to control by physical and chemical factors.

A scheme is proposed that illustrates compensatory use of energy for processes controlling dormancy induction and germination. A block of germination, e.g. by low water potential polyethylene glycol solution or a supraoptimal temperature spares energy to be utilized for dormancy induction while a block of dormancy induction by low levels of CN⁻ (similar to GA and light effects) drives germination. Blocking both processes by inhibitors (e.g. CN⁻, CN⁻ + SHAM) presumably leads to accumulation of `reducing power' with consequent improvement in O₂ uptake and oxidation rates of processes controlling germination or dormancy induction upon removal of the inhibitors.

     

Nucleotide sequence analysis and enhancer function of long terminal repeats associated with an endogenous African green monkey retroviral DNA.

The nucleotide sequence and enhancer activity of the long terminal repeats (LTRs) associated with a cloned endogenous African green monkey (AGM) retroviral DNA designated as lambda-AGM-1 was studied. A unique feature of the endogenous AGM proviral LTRs was the presence of multiple copies of two types of directly repeating units in the U3 region: 16 8-base-pair (bp) repeats were present in the 5' LTR and 12 were present in the 3' LTR which were bound by a 6-bp perfect direct repeat; tandem duplication of a 32-bp sequence resulted in 3.5 copies in the 5' LTR and 2.5 copies in the 3' LTR. Nucleotide sequence homology was seen between the 8-bp direct repeats located in the AGM proviral LTRs and a 10-bp repeat unit of the deca-satellite present in AGM cellular DNA. The 32-bp repeats of the AGM proviral LTRs contained sequences which were related to the SV40 21-bp repeats and to the "core" of the SV40 72-bp enhancer element. Furthermore, the AGM provirus was distinct from known infectious retroviruses due to the presence of a primer-binding sequence complementary to the 3' terminus of mammalian tRNAGly. Functional analysis of the 3' LTR present in lambda-AGM-1 DNA by chloramphenicol acetyltransferase assay demonstrated enhancer activity associated with the 32-bp direct repeats. Sequences outside the 32-bp unit were necessary for full activator function, suggesting the presence of multiple enhancer domains in the AGM provirus.     

Role of verocytotoxigenic Escherichia coli in cattle and buffalo calf diarrhoea

Abstract 273 Strains of Escherichia coli isolated from diarrhoeic and healthy control cattle and buffalo calves in Sri Lanka, were tested for Verocytotoxin (VT) and for heat-stable (ST) and heat-labile (LT) enterotoxins. VT and ST toxigenic E. coli were significantly associated with diarrhoea, accounting for 28% and 18% of diarrhoeic episodes, respectively. LT toxigenic E. coli were not significantly associated with diarrhoea.