Detection of enterotoxigenic Staphylococcus aureus in dried skimmed milk: use of the polymerase chain reaction for amplification and detection of staphylococcal enterotoxin genes entB and entC1 and the thermonuclease gene nuc

The polymerase chain reaction was used to amplify the staphylococcal enterotoxin B and C genes (entB and entC1) and the staphylococcal nuclease gene (nuc). Two sets of primers ("nested primers") were found to be necessary for the detection of low copy numbers of purified DNA in diluent. These allowed detection of ca. 1 fg of purified target DNA, while 100 pg was required before detection of entB, entC1, and nuc with single primer pairs was possible. With nested primers, enterotoxigenic Staphylococcus aureus cells could be detected in artificially contaminated dried skimmed milk samples at levels of ca. 10(5) CFU ml-1 within 8 h. No cross-reaction was observed between the highly homologous entB and entC1 genes. The method showed total specificity for entC1 when tested against a wide variety of other bacteria.     

Poliovirus antigen chimeras.

Poliovirus, the aetiological agent of paralytic poliomyelitis, is arguably the best characterized of all animal viruses. Using recombinant-DNA technology, this information, together with the availability of infectious cDNA clones of the notably safe and efficacious live attenuated Sabin 1 vaccine strains of poliovirus, has enabled the creation of hybrid viruses (chimeras) possessing novel antigenicity. The potential applications of these 'epitope-presentation systems' include their use as immunogens, as antigens for serodiagnosis, and as vaccines.     

Direct observation by X-ray analysis of the tetrahedral "intermediate" of aspartic proteinases.

We report the X-ray analysis at 2.0 A resolution for crystals of the aspartic proteinase endothiapepsin (EC 3.4.23.6) complexed with a potent difluorostatone-containing tripeptide renin inhibitor (CP-81,282). The scissile bond surrogate, an electrophilic ketone, is hydrated in the complex. The pro-(R) (statine-like) hydroxyl of the tetrahedral carbonyl hydrate is hydrogen-bonded to both active-site aspartates 32 and 215 in the position occupied by a water in the native enzyme. The second hydroxyl oxygen of the hydrate is hydrogen-bonded only to the outer oxygen of Asp 32. These experimental data provide a basis for a model of the tetrahedral intermediate in aspartic proteinase-mediated cleavage of the amide bond. This indicates a mechanism in which Asp 32 is the proton donor and Asp 215 carboxylate polarizes a bound water for nucleophilic attack. The mechanism involves a carboxylate (Asp 32) that is stabilized by extensive hydrogen bonding, rather than an oxyanion derivative of the peptide as in serine proteinase catalysis.     

Discrimination of the sign of frequency differences bySternopygus,an electric fish without a jamming avoidance response

Several species of weakly electric fish reflexively change their frequency of electric organ discharge (EOD) in response to sensing signals of similar frequency from conspecifics; that is, they exhibit jamming avoidance responses (JAR).Eigenmannia increases its EOD frequency if jammed by a signal of lower frequency and decreases its EOD frequency if jammed by a signal of higher frequency. This discrimination is based on an analysis of the patterns of amplitude modulations and phase differences resulting from signal interference. Fish of the closely related genus,Sternopygus, however, do not exhibit a JAR. Here we show that despite lacking this behavior,Sternopygus shares many sensory processing capacities withEigenmannia:

C3 allotypes in pregnancy hypertension and eclampsia

C3 allotyping has been performed on 424 Australian women, 203 with normotensive pregnancies, 161 with hypertensive noneclamptic pregnancies and 60 eclamptic women. The frequency of women heterozygous for 'rare' C3 alleles was 1% in the normotensive women and 3.7% in the hypertensive group. Three out of 25 (12%) of the women with proteinuric hypertension in pregnancy carried 'rare' C3 alleles. This suggested the hypothesis that pre-eclampsia/eclampsia is associated with a higher frequency of rare alleles. The sample of 60 eclamptic women collected to test the hypothesis had no rare alleles, refuting the hypothesis. The frequency of the common (C3F, C3S) alleles did not differ significantly between the three groups. We conclude that there is no evidence for any association between susceptibility to eclampsia and allotypes of the C3 complement component.     

Evaluation of methods for the isolation of plasma membranes displaying guanosine 5'-triphosphate-dependence for the regulation of adenylate cyclase activity: potential application to the study of other guanosine 5'-triphosphate-dependent transduction systems

The GTP-dependence for stimulatory and inhibitory regulation of plasma membrane adenylate cyclase activity was measured in plasma membrane fractions isolated from a variety of cell types (platelets, lymphocytes, PC12 cells, GH3 cells, NBP2 cells, and hepatocytes). This report shows that the isolation of plasma membranes for the study of GTP-dependent adenylate cyclase activity was, for some cells, enhanced by the exposure of the cells to glycerol prior to cell lysis. The isolation of plasma membranes from other cells, which did not appear to be sensitive to glycerol pretreatment, was enhanced by the removal of heavy particulate matter prior to fractionation of the cell lysate. The regulation of enzyme activity by various agents was found to be dependent upon the presence of (exogenous) GTP to varying degrees, indicating variable contamination of membrane preparations with GTP. It is concluded that (i) exposure of platelets and lymphocytes to glycerol prior to cell lysis decreases subsequent contamination of the plasma membrane preparation with GTP, and (ii) although glycerol pretreatment of other cells does not ensure the subsequent isolation of plasma membrane adenylate cyclase activity displaying high requirements for (exogenous) GTP, it is a reasonable first approach to be used during the development of procedures for the isolation of plasma membranes.     

Sexual coloration, plasma concentrations of sex steroid hormones, and responses to courtship in the female keeled earless lizard (Holbrookia propinqua)

The reproductive condition, steroid hormone concentrations in the plasma, and behavior of bright and plain female Holbrookia propinqua were examined. Bright females performed significantly more aggressive rejection of courtship than plain females. Bright females were significantly more likely than plain females to have follicles larger than 5.0 mm or oviductal eggs; females with large follicles or oviductal eggs had significantly higher concentrations of progesterone and androgen than those with small follicles and lacking oviductal eggs. Plasma progesterone, androgen, and estradiol levels in the females studied behaviorally were significantly higher for the bright females than for the plain ones. Females undergoing rapid brightening were significantly more likely to be sexually receptive and copulate than were either plain or fully brightened females. The role of sex steroid hormones in coloration and behavior and the adaptive value of chromatic signalling by females are discussed.     

Quantitative analysis of immunogold labelling for ferritin in liver from control and iron-overloaded rats

Summary The distribution of ferritin antigenicity in control and iron-loaded rat hepatocytes was investigated with an immunogold-ferritin antibody technique. Antibody to horse spleen ferritin showed immunoreactivity as determined by dot blotting with immunogold/silver staining with purified rat liver ferritin but not with rat haemosiderin. The initial site of ferritin degradation was studied by analysing the density of gold labelling in the cytosol and lysosomes in combination with pre-embedding acid phosphatase cytochemistry.Immunoreactive ferritin was present in the cytosol, cytosolic clusters and lysosomes of normal hepatocytes. After iron-loading, the labelling density increased over tenfold in parenchymal cell cytosol with a smaller increase in Kupffer cells. Ferritin clusters contained substantially more immunoreactive ferritin than equivalent areas of lysosomes or cytosol. Analysis of the labelling density in hepatocyte lysosomes showed that, despite a striking increase in iron content, one-quarter of the lysosomes showed less immunolabelled ferritin than the cytosol. The existence of a wide range of ferritin labelling densities in the lysosomes with a large proportion unlabelled suggests that the ferritin protein shell is not degraded at a significant rate either in the cytosol or in clusters but only after incorporation into lysosomes.     

Molecular cloning, expression, and analysis of the genes of the homoprotocatechuate catabolic pathway of Escherichia coli C.

The molecular cloning and fine-structure analysis of the homoprotocatechuate (hpc) catabolic pathway genes of Escherichia coli C are described. The genes were located in two operons, hpcBCDEF and hpcGH, that were very closely linked. A regulatory gene, hpcR, involved in the expression of both operons was also identified. Various subclones isolated in the study were useful in the production of chemical intermediates of the pathway. The availability of one such compound facilitated the discovery of a previously unrecognized isomerase involved in the catabolic sequence.