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Biomedical subjects

J Davison

Publications and source records attributed to J Davison.

At least 73 records · Page 4Linked to original sources
PubMed1980

Cloning and expression of Trypanosoma brucei kinetoplast DNA in Escherichia coli.

The kinetoplast DNA of Trypanosoma brucei is made of two components: mini-circles (1 kb, 90% of total kDNA) and maxi-circles (20 kb, 10%) of total kDNA). These are interlocked to form a network of about 10 000 kb. In order to analyse the components of such a network structure, we have cloned individual mini-circle molecules and two of the three EcoRI maxi-circle fragments in E. coli. Cloned mini-circles are somewhat heterogeneous in size and their restriction patterns are completely different. Despite this heterogeneity all are found to contain a homologous region(s) defined by DNA/DNA hybridization. The maxi-circles probably correspond to the mitochondrial DNA of other organisms and, in contrast to mini-circles, do not show sequence heterogeneity. One of the two cloned maxi-circle EcoRI fragments is able to direct the synthesis of two polypeptides of 10 300 and 13 500 daltons in E. coli mini-cells. Detailed analysis of this phenomenon shows that both structural genes and promoter(s) are located within the cloned maxi-circle fragment.

Animals↗
PubMed1980

Prediction of abnormal umbilical cord position and intrapartum cord problems from the nonstress test.

A prospective analysis of the nonstress test revealed a group of patients who demonstrate typical variable decelerations associated with fetal movement. Such variable decelerations were observed only in patients who had the test performed for suspected intrauterine growth retardation or for postdatism. Almost half of the suspected small-for-gestational-age fetuses and fetuses of a postdate gestation who demonstrated variable deceleration at nonstress testing also demonstrated an umbilical cord in an abnormal position at delivery. The position of the cord in utero of the remaining patients with variable deceleration at nonstress testing was not determined; however, 88% of this group demonstrated significant variable deceleration during labor. An abnormally positioned cord was noted in half of the patients undergoing cesarean section. It appears that patients with small-for-gestational-age fetuses and those with postdate gestation are at higher risk of intrapartum cord compression problems when variable decelerations are noted with fetal movements during a nonstress test.

Female↗
PubMed1979

Self-monitoring of blood glucose in diabetic pregnancy.

Admission to hospital is usually recommended to achieve the best possible diabetic control during pregnancy. We have used blood glucose monitoring at home to find out if patients can achieve equally good control outside hospital. Twenty-five consecutive diabetic patients were studied, of whom 20 had taken insulin before pregnancy. Six of their 14 previous pregnancies had ended in perinatal death. The 25 women performed 4247 blood glucose measurements during their pregnancies. Overall the mean blood glucose concentration was 7.1 mmol/l (128 mg/100 ml); before meals the mean was 6.5 mmol/l (117 mg/100 ml). Mean concentrations were lower in the third trimester, but at no stage was control in hospital significantly better than at home. The mean hospital stay before delivery was 22 days, and all patients had live babies. Monitoring blood glucose concentrations at home produces greater understanding and motivation among patients, improves control early in pregnancy, and shortens time spent in hospital.

Adolescent↗
PubMed1979

Cloning of bacteriophage T5 DNA fragments in plasmid pBR322 and bacteriophage lambda gtWES.

Bacteriophage T5 was digested with the restriction endonucleases HindIII and EcoRI and the resulting fragments were inserted into the plasmid pBR322 and the bacteriophage lambda gtWES as vectors. Approx. 15% of the phage genome was recovered in recombinant clones. The recombinants were characterized by restriction analysis, DNA/DNA hybridization employing Southern blots, and ability to complement or recombine with amber mutants of T5. The results obtained allow revisions of the physical map of the T5 genome and partial correlation of the physical map with the genetic map.

Chromosome Mapping↗
PubMed1979

A new host-vector system allowing selection for foreign DNA inserts in bacteriophage lambda gtWES.

An improved vector (lambda gtWES.T5-622) for EcoRI fragments has been derived from EK2 vector lambda gtWES.lambdaB' by replacing the lambda B fragment with two identical 1.1 Md fragments from the pre-early region of bacteriophage T5. The new vector has two advantages which facilitate elimination of parental-type recombinants in an in vitro recombination experiment. Firstly, the 1.1 Md insert is too small to be re-inserted into lambda gtWES in a single copy. Secondly the 1.1 Md T5 fragment carries T5 gene A3 which prevents growth of phage retaining this fragment when the Excherichia coli host carries plasmid ColIb. Thus, essentially all plaques are due to phage with donor DNA inserts and are free of T5 DNA fragments. The size usually given as the theoretical minimum size for insertion into the lambda gt series of vectors is 0.66 Md. We have shown that this size is an underestimate and that the lower limit is about 1.6 Md. A precise estimate is difficult since there is strong selection, among phage having small inserts, for those which have acquired additional genetic material by duplication of the lambda DNA.

Bacteriophage lambda↗
PubMed1979

Restriction insensitivity in bacteriophage T5 I. Genetic characterization of mutants sensitive to EcoRI restriction.

Unmodified bacteriophage T5 is able to grow normally on bacterial hosts carrying three different Escherichia coli restriction systems, EcoK, EcoPI, and EcoRI. Under the same conditions, the plating efficiency of bacteriophage gamma is less than 10(-9). At least in the case of EcoRI, this lack of in vivo restriction is not due to lack of restriction sites on the T5 DNA molecule. These observations suggest that bacteriophage T5 specifies one or more restriction protection systems. Mutants (ris) of T5 have been isolated which confer sensitivity to EcoRI restriction but not to EcoK or EcoPI. The mutations are located in the pre-early region of the genetic map but are too far apart to be alleles of a single gene. Complementation studies show that the ris mutants can be helped to grow on the EcoRI-restricting host by coinfection with T5+. This result provides evidence for a restriction protection function but does not necessarily show that the ris mutants are defective in such a system.

Coliphages↗
PubMed1979

Restriction insensitivity in bacteriophage T5. II. Lack of EcoRI modification in T5+ and T5ris mutants.

Neither bacteriophage T5+ nor its EcoRI-sensitive ris mutants became modified during growth on an EcoRI-modifying host. For this reason, the rare ris plaques able to grow on the EcoRI-modifying host were always due to revertant phage rather than to modified ris mutants. The ris mutations resulted in the creation of new EcoRI cleavage sites in the terminally repetitious first-step transfer DNA, and analysis of T5 ris revertants showed loss of these sites and restoration of the wild-type restriction pattern. Natural EcoRI sites present in the second-step transfer DNA were never lost in T5ris revertants, indicating that these are irrelevant to in vivo restriction and are protected during growth on the restricting host.

Coliphages↗
PubMed1977

Properties of permissive monkey cells transformed by UV-irradiated simian virus 40.

African green monkey cells (CV1 line) were infected with UV-irradiated simian virus 40 (SV40), and permissive lines of stably transformed cells were established. These cell lines display the SV40 T-antigen and the growth characteristics typical of nonpermissive transformed cells (e.g., reduced cell density inhibition, reduced serum dependence, ability to overgrow normal cells, and colony formation in soft agar). The level of permissiveness to superinfecting SV40 is fully comparable with that of nontransformed CV1 and BSC-1 lines. The transformed monkey lines also support SV40 plaque production under agar. By Cot analysis, the transformed permissive cells contain, on an average, 1 to 2 SV40 genome equivalents, and the majority of the viral sequences are associated with the high-molecular-weight cellular DNA. No spontaneous production of infectious SV40 has been observed. The transformed permissive monkey cells failed to support the replication of SV40 tsA mutants at the restrictive temperature. To account for this, it is suggested that the gene A product has separate functions for transformation and initiation of viral DNA synthesis, and only the former function is expressed in the transformed permissive monkey cells.

Animals↗
PubMed1977

Health indexes sensitive to medical care variation.

Data from the fifteen Hospital Regions of England and Wales were used to determine the utility of health outcome indexes, derived from existing health statistics, for monitoring the quality and effectiveness of health services. Outcome measures reflect not only the impact of the system of care but also the sociodemographic characteristics of the population. An attempt therefore was made to identify those outcome measures most sensitive to variations in medical care and least affected by sociodemographic differences. In general, most indexes examined in this paper appear to be more sensitive to variations in the sociodemographic characteristics of the population. However, thosoutcome measures related to provision of care in hospital appear to relatively more sensitive to variation in medical care than those which are community based. This suggests that, at least for monitoring the effectiveness of medical care in the community, it may be necessary to move away from the more "traditional" health indexes toward measures that take into consideration the different patterns of care and the social and behavioral aspects of health.

Analysis of Variance↗
PubMed1976

Hydra hymanae: regulation of the life cycle by time and temperature.

Hydra hymanae, a hermaphroditic freshwater coelenterate, reproduces asexually at 24 degrees C and sexually at 15 degrees C. The appearance of gonads begins 12 days after transfer from 24 degrees to 15 degrees C and is complete 35 days after the temperature transition. Testes appear before eggs. Fifty percent of the mature embryos maintained at 15 degrees C hatch by day 61, but they have a low level of survival. Fifty percent of the mature embryos pretreated for from 5 to 25 days at 4 degrees C hatch by about day 45, and these have a high level of survival. Embryos maintained at 4 degrees C for longer periods (55 to 85 days) accumulate in a prehatching state and hatch with a high degree of synchrony approximately 7.5 days after return to 15 degrees C. Populations derived from newly hatched polyps are refractory to sex induction for approximately 120 days. The system is well adapted to ensure a regular alternation of reproductive modes in the natural environment.

Age Factors↗
PubMed1975

Bacterial mutants able to partly suppress the effect of N mutations in bacteriophage lambda.

A method is described whereby bacterial mutants (sun) may be selected which are able to specifically suppress mutations in the N gene of bacteriophage lambda. The sun mutations seem to be allelic to suA mutations, which suppress the polarity of nonsense codons, since suA mutants have all of the properties of sun mutants and both are genetically linked to the ilv gene. In the light of these experiments and recent data by others, models originally suggested to explain polarity in bacterial operons, are discussed with regard to their possible relevance to the mechanism of N action.

Bacteriophage lambda↗
PubMed1973

Population growth in planaria Dugesia tigrina (gerard). Regulation by the absolute number in the population.

Planaria reproduce by transverse fission. Isolated worms increase in number exponentially, while social animals at the same density are inhibited in terms of numerical increase, but over a 25 day period undergo a larger increase in mass. Isolated posterior fission products reproduce faster than isolated anterior fission products. Regulation of population growth is independent of density over a 16-fold range and regulatory factors cannot be demonstrated in the medium. Regulation of population growth depends on direct contact between animals. Fission period varies from individual to individual and from period to period for a given individual. Doubling time is related to the absolute number of individuals comprising the population as follows: P(N) = (P(M) . N)/(K + N), where P(N) is the doubling period of a population of N individuals, P(M) is the doubling time of an infinitely large population, N is the number of individuals in the population, and K is the number of individuals in a population the period of which is one-half P(M). At 22 degrees -24 degrees C P(M) is estimated to be 43.3 days and K is 1.87 individuals. A model system assumes that inhibitor flows through the population from animal to animal from the slowest to the fastest animal in the population thus acting to synchronize population increase as well as to determine the rate of population growth. A possible source of the inhibitor is discussed.

Animals↗