Cloning of aroG, the gene coding for phospho-2-keto-3-deoxy-heptonate aldolase(phe), in Escherichia coli K-12, and subcloning of the aroG promoter and operator in a promoter-detecting plasmid

Defective transducing phages carrying aroG, the structural gene for phenylalanine (phe)-inhibitable phospho-2-keto-heptonate aldolase (EC 4.1.2.15; previously known as 3-deoxy-D-arabinoheptulosonate-7-phosphate synthetase[phe]), have been isolated, and DNA from two of these phages has been used to construct a restriction map of the region from att lambda to aroG. A 7.6-kb PstI-HindIII fragment from one of these phages was cloned into pBR322 and shown to contain aroG. The location of aroG within the 7.6 kb was established by subcloning and Tn3 transpositional mutagenesis. A fragment carrying the aroG promoter and operator has been cloned into a high copy number promoter-cloning vector (pMC489), and the resulting aroGpo-LacZ' (alpha) fusion subcloned in a low copy number vector. Strains with this fusion on the low copy number vector exhibit negative regulation of beta-galactosidase expression by both phenylalanine and tryptophan and positive regulation by tyrosine in a tyrR+ background.     

Action of pilocarpine on the normal frog heart and in pathology

Experiments on frogs were performed to examine the effect of the M-cholinomimetic pilocarpine on the heart. It was discovered that at concentrations of 10(-15)--10(-5) g/ml pilocarpine exerted only an adverse chronotropic effect on the perfused heart. When applied at a concentration of 10(-4) g/ml the drug produced a negative as well as a positive chronotropic effect. The latter occurred spasmodically (without progressive rise in the heart rate) in association with a slow heart rate. In some experiments such effects were preceded by a certain deceleration of the heart. In experiments with positive chronotropic effects, arrhythmias and sinoatrial dissociation were observed sometimes. Experiments with recording of the electrograms of the sinuses and lower parts showed that such effects were caused not by pacemaker acceleration but by the removal of the blockade of conduction, between the pacemaker and the atria. As far as the pacemaker is concerned, pilocarpine exerted only a negative chronotropic effect.     

A rapid single-stranded cloning strategy for producing a sequential series of overlapping clones for use in DNA sequencing: application to sequencing the corn mitochondrial 18 S rDNA

A simple new procedure was described for producing a sequential series of overlapping clones for use in DNA sequencing. The technique used single-stranded M13 DNA and complementary DNA oligomers to form specific cleavage and ligation substrates. It was, therefore, independent of the sequence of the DNA cloned into the vector. Deletions of varying sizes were generated from one end of the insert through the 3' to 5' exonuclease activity of T4 DNA polymerase. The approximate size of the deletion and therefore the starting point for DNA sequencing could be estimated by electrophoresis of the subcloned phage DNA on a agarose gel. This greatly reduced the number of templates that must be sequenced to obtain a complete sequence. The entire procedure could be carried out in one tube in less than a day. The procedure was used to subclone and sequence the maize mitochondrial 18 S rDNA and 5' flanking region (2622 bases) in less than a week. Other applications of oligomers and single-stranded DNA in the construction of insertions, deletions, and cDNAs are discussed.     

Effect of the lymphocytosis-stimulating factor from Bordetella pertussis on murine lymphoid and hemopoietic cells

Effect of B. pertussis lymphocytosis-promoting factor (LPF) on the lympho-hematopoietic system of mice was studied. The injection of LPF was shown to sharply enhance endogenous colony formation and to induce a severe depletion of thymus cells, reaching its maximum of day 4. Thymocytes obtained on day 2 or 3 after the injection of LPF produced a suppressive effect on endogenous colony formation. The proliferative activity of hematopoietic stem cells sharply increased under the influence of LPF, though it had no radioprotective action. On the following day after the injection of LPF a steep rise in the number of hematopoietic stem cells was observed in the blood of mice: their content increased 20-fold in comparison with the control level. These data may be important for the evaluation of the side effects of pertussis vaccine on the lympho-hematopoietic system.     

The cluster method in conducting epidemiological research

The Expanded Programme on Immunization (EPI) whose goal is to reduce morbidity and mortality by providing children with immunizations against diphtheria, pertussis, tetanus, poliomyelitis, measles, and tuberculosis continually faces the problem of documenting immunization coverage rates. Therefore the EPI seeks simple, effective, and inexpensive methods of evaluation which could be implemented in different countries. An example of such a method is a simplified cluster sampling technique of estimation of immunization coverage through the examination of 210 children, selected randomly as 30 groups of 7 children each. In 1978-1984 more than 1000 immunization coverage surveys were performed all over the world, mainly in developing countries. In a modified way this method is also used to collect data on morbidity and mortality of certain EPI target diseases as well as diarrhoeal diseases.     

Characterization of staphylococci

A total of 158 Staphylococcus strains from various sources were characterized by biochemical, physiological, and morphological tests. Numerical taxonomy was applied by using these features. Taxonomic analysis was done with programs run under the MVS-TSO system of the IBM 370 complex and PDP-10 system of the National Institutes of Health. DNA-DNA hybridization with nitrocellulose filters was done to compare selected atypical cultures with American Type Culture Collection reference strains. We found that the use of the nomenclature of Bergey's Manual (8th edition) to identify these strains by species was not adequate. DNA homology values supported the formation of Staphylococcus hyicus subsp. hyicus separate from Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus. The three tests that best separated these strains into four species were (i) tube coagulase (6-h or 24-h porcine plasma or 24-h Difco rabbit plasma), (ii) production of acetoin or acid aerobically from ribose, maltose, or trehalose, and (iii) growth in the presence of novobiocin. Four strains of S. hyicus subsp. hyicus (VII76, VII113, VII131, and VA519) gave typical enterotoxigenic responses in monkey-feeding tests but were negative for enterotoxins A through E, suggesting the presence of one or more new enterotoxins. Two coagulase-negative, heat-stable DNase-positive strains (D143 and ARM) could not be classified by either DNA-DNA hybridization or numerical taxonomy, and D143 was enterotoxigenic as measured by the monkey-feeding bioassay. DNA homology showed that strain FRI-698M was more closely related to S. epidermidis than to S. aureus, yet it produced enterotoxin D. These data suggest the occurrence of coagulase-negative enterotoxigenic strains that are not S. aureus; nonetheless, a positive tube coagulase test and heat-stable DNase test should together be useful for routine screening of most potentially enterotoxigenic staphylococci in foods.     

Relations between synthesis of deoxyribonucleotides and DNA replication in 3T6 fibroblasts

In exponentially growing 3T6 cells, the synthesis of deoxythymidine triphosphate (dTTP) is balanced by its utilization for DNA replication, with a turnover of the dTTP pool of around 5 min. We now investigate the effects of two inhibitors of DNA synthesis (aphidicolin and hydroxyurea) on the synthesis and degradation of pyrimidine deoxynucleoside triphosphates (dNTPs). Complete inhibition of DNA replication with aphidicolin did not decrease the turnover of pyrimidine dNTP pools labeled from the corresponding [3H]deoxynucleosides, only partially inhibited the in situ activity of thymidylate synthetase and resulted in excretion into the medium of thymidine derived from breakdown of dTTP synthesized de novo. These data demonstrate continued synthesis of dTTP in the absence of DNA replication. In contrast, hydroxyurea decreased the turnover of pyrimidine dNTP pools 5-50-fold. Hydroxyurea is an inhibitor of ribonucleotide reductase and stops DNA synthesis by depleting cells of purine dNTPs but not pyrimidine dNTPs. Our results suggest that degradation of dNTPs is turned off by an unknown mechanism when de novo synthesis is blocked.