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Biomedical subjects

I Roberts

Publications and source records attributed to I Roberts.

At least 235 records · Page 13Linked to original sources
PubMed1993

Analysis of the tumorigenic potential of common marmoset lymphoblastoid cells expressing a constitutively activated c-myc gene.

The respective roles of Epstein-Barr virus (EBV) and c-myc in the pathogenesis of endemic Burkitt's lymphoma (BL) are unclear. In order to help resolve the question whether constitutive expression of the c-myc gene in an EBV-immortalised B cell is sufficient to induce a tumorigenic phenotype, B cells from a common marmoset (Callithrix jacchus) were immortalised with EBV, transfected with a constitutively activated c-myc gene and inoculated into the host animals. Despite the cell line transfected with c-myc displaying enhanced growth characteristics, in vitro and in vivo experiments demonstrated that this was not sufficient to induce a tumorigenic phenotype. This supports our previous findings with EBV-immortalised human B cells transfected with an activated c-myc gene (Hotchin et al., 1990).

Animals↗
PubMed1993

Effect of exposure measurement error in a case-control study of child pedestrian injuries.

We examined the effect of the duration of the exposure measurement period on the odds ratio in a case-control study of traffic flow and the risk of child pedestrian injury. Varying the length of the measurement period resulted in differential exposure misclassification and bias in the odds ratio. Differential misclassification may have arisen from measurement error in traffic flow estimation over a short period or from inclusion of irrelevant exposure information with a longer measurement period.

Accidents, Traffic↗
PubMed1993

Non-traffic child pedestrian injuries.

All non-traffic child pedestrian deaths and injuries resulting in hospitalization in the Auckland region over a 5 year period were identified from coroner's and hospital records. There were eight deaths (0.77/100,000 children per year) and 91 hospital admissions (8.7/100,000 children per year). Close to half (48%) of the non-traffic pedestrian injury admissions had been misclassified as traffic pedestrian injuries. Eighty-seven per cent of the non-traffic pedestrian injury deaths and 93% of the injuries occurred in residential driveways, most often involving a child run over by a reversing vehicle. Further studies are required to determine the most effective strategies for the prevention of non-traffic child pedestrian injuries.

Accidents↗
PubMed1993

In vivo regulatory responses of four Escherichia coli operons which encode leucyl-tRNAs.

Four Escherichia coli operons, the leuV operon which encodes tRNA(1Leu), the leuX operon which encodes tRNA(6Leu), the metT operon which encodes tRNA(3Leu), and the argT operon which encodes tRNA(1Leu), were examined for the stringent response induced by serine hydroxamate and for growth rate-dependent regulation. In nuclease protection assays, the leuV operon displayed the stringent response in response to leucine starvation, analog inhibition, and growth of a temperature-sensitive leucyl-tRNA synthetase mutant at nonpermissive temperatures. The leuV operon also exhibited the stringent response in multicopy plasmids. The promoters of all four leucyl operons were fused to the gene for beta-galactosidase and inserted into the chromosome by using bacteriophage lambda. All except the leuX promoter displayed growth rate-dependent regulation, consistent with the recent report that the concentration of tRNA(6Leu) actually decreases as growth rate increases. The leuV promoter fused to the beta-galactosidase gene showed a decrease in efficiency in the presence of extrachromosomal copies of rRNA genes. All chromosomal tRNA genes examined showed decreased transcriptional activity following a stringent response, but the leuX gene responded to a lesser extent (3-fold versus 10-fold or more) than the others. Primer extension analysis of this promoter showed little if any response to serine hydroxamate treatment, suggesting that multiple levels of control may exist or that promoter context effects are important in regulation.

Base Sequence↗
PubMed1992

Genome diversity at the serA-linked capsule locus in Escherichia coli.

Individual isolates of Escherichia coli synthesize one of more than 70 chemically distinct polysaccharides which form the capsule. In this article we review the genetics of capsule production in E. coli and highlight what this is beginning to reveal in terms of the genetic basis of the structural diversity of polysaccharides. The serA-linked capsule locus can take three different allelic forms. Two of these are associated with capsule genes and are themselves internally variant, whilst the third form has not so far been implicated in capsule biogenesis. Thus the serA-linked region of the E. coli genome is strikingly polymorphic.

Carbohydrate Dehydrogenases↗
PubMed1992

Child passenger fatalities and restraint use in Auckland.

AIMS: To determine the proportion of children killed as passengers in car crashes who were unrestrained and to estimate the reduction in mortality that might result from increasing child restraint utilisation. METHODS: All children killed as passengers in car crashes, over the period 1980-90, were identified from the Auckland coroners records. Data were recorded on sex, age, use and type of restraint, position within the motor vehicle, pattern of injuries and place of death. RESULTS: There were 49 children (25 male, 24 female) killed as passengers in car crashes over the study period (2.14/100,000/year). The median age was eight years (range 0-14 years). Of the 38 children for whom restraint use could be determined, 31 (81.6%) were unrestrained and seven (18.4%) were restrained. None of the children aged 0-2 years were restrained. Thirty-five children (71.4%) died at the scene of the crash, three (6.2%) died during transport to hospital, and 11 (22.4%) died in hospital. CONCLUSIONS: Based on overseas reports of the efficacy of child restraints, close to half (49%) of all child passenger deaths in Auckland could have been prevented with appropriate child restraint use.

Accidents, Traffic↗
PubMed1992

Structural requirements for tRNA methylation. Action of Escherichia coli tRNA(guanosine-1)methyltransferase on tRNA(1Leu) structural variants.

The Escherichia coli enzyme tRNA(m1G)methyltransferase, one of a group of post-transcription tRNA-modifying enzymes, shows remarkable specificity in selecting the tRNA species and the specific guanosine base to be methylated. To examine the structural basis of this specificity, we synthesized a total of 15 modifications of tRNA(1Leu) and measured their methylation reaction kinetics in vitro. Elimination of any one of the three tRNA side loops, the V loop, the T loop, or the D loop, reduced the Vmax for methylation by about 1 order of magnitude. Elimination of all three side loops reduced Vmax by about 2 orders of magnitude. Clearly, gross tRNA structure is important for full enzyme activity. At the bottom of the stem proximal to the anticodon loop, in the pair at positions 31-39, substitution of a G-C for a C-G, a change that should not weaken the helical structure, had little effect on Vmax or Km. However, substitution of a G for a C increased Vmax and Km, whereas substitution of a C for G sharply reduced Vmax and, to a lesser extent, Km. These results appear to be a consequence of the principle that purines are better than pyrimidines in the stacking of adjacent bases for stability. Stacking in the stem structure appears to be important for methylation enzyme activity. In the anticodon loop itself, changing a U to a C had little effect, but changing the G of the anticodon to a C reduced Vmax over 20-fold, demonstrating the importance of the presence of the anticodon G adjacent to the G being methylated for enzyme recognition.

Anticodon↗
PubMed1992

Child pedestrian injury 1978-87.

OBJECTS: to report the incidence of child pedestrian injury in New Zealand and review prevention strategies. METHODS: examination of National Health Statistics Centre mortality and public hospital morbidity data from 1978-87. RESULTS: over the ten year period, there was an annual average of 30 deaths (3.6/100,000 per year) and 411 hospitalisations (49.4/100,000 per year) for child pedestrian injury. There has been no significant reduction in the fatality or hospital morbidity rate over this time. Pedestrian fatality rates are highest for boys and for children in the youngest age groups. Hospitalisation rates are over 2.5 times higher for Maori children than for nonMaori children. CONCLUSIONS: child pedestrian injury is an important public health problem in New Zealand for which there are few established prevention strategies. Controlled studies aimed at the identification of modifiable environmental factors are required.

Accidents, Traffic↗
PubMed1992

An area analysis of child injury morbidity in Auckland.

The geographical distribution of child injury morbidity in Auckland between 1982 and 1987 was examined. Analysis of total injury, pedestrian injury and vehicle occupant injury, with the census area unit as the basic spatial entity revealed distinct variations in child injury morbidity by census area unit. Morbidity rates were above average in parts of the central urban area and South Auckland and below average on the North Shore. Total injury morbidity and pedestrian injury morbidity rates were strongly correlated with census area unit unemployment rates, which were used as a measure of socio-economic deprivation. Geographical areas with high rates of child injury morbidity, to which injury prevention resources can be directed, were identified. In particular, the results suggest that injury prevention programmes should be targeted at socio-economically disadvantaged communities.

Accidents, Traffic↗
PubMed1992

Homology among Escherichia coli K1 and K92 polysialytransferases.

The neuS-encoded polysialytransferase (polyST) in Escherichia coli K1 catalyzes synthesis of polysialic acid homopolymers composed of unbranched sialyl alpha 2,8 linkages. Subcloning and complementation experiments showed that the K1 neuS was functionally interchangeable with the neuS from E. coli K92 (S. M. Steenbergen, T. J. Wrona, and E. R. Vimr, J. Bacteriol. 174:1099-1108, 1992), which synthesizes polysialic acid capsules with alternating sialyl alpha 2,8-2,9 linkages. To better understand the relationship between these polySTs, the complete K92 neuS sequence was determined. The results demonstrated that K1 and K92 neuS genes are homologous and indicated that the K92 copy may have evolved from its K1 homolog. Both K1 and K92 structural genes comprised 1,227 bp. There were 156 (12.7%) differences between the two sequences; among these mutations, 55 did not affect the derived primary structure of K92 polyST and hence were synonymous with the K1 sequence. Assuming maximum parsimony, another estimated 17 synonymous mutations plus 84 nonsynonymous mutations could account for the 70 amino acid replacements in K92 polyST; 36 of these replacements were judged to be conservative when compared with those of K1 polyST. There were no changes detected in the first 146 5' or last 129 3' bp of either gene, suggesting, in addition to the observed mutational differences, the possibility of a past recombination event between neuS loci of two different kps clusters. The results indicate that relatively few amino acid changes can account for the evolution of a glycosyltransferase with novel linkage specificity.

Amino Acid Sequence↗
PubMed1991

Critical injuries in paediatric pedestrians.

Data are presented on all sixty-four children who were injured as pedestrians and admitted to the department of critical care medicine, Auckland Hospital over a four year period. Median age was six years, with a male:female ratio of 1.6:1.0. Admission rates were 3.1 and 3.0 times higher for Maori and Pacific Island children, respectively, than for children of European origin. Fifty-two percent of injuries occurred between 3 pm and 7 pm. Median injury severity score (ISS) was 29, and 95% of patients had an ISS of 16 or more. Life threatening injuries were most commonly to the head, whilst less severe injuries, commonly fractures, were to the limbs. The combination of head and lower limb injury was seen in 53% of patients. Twenty-nine patients had 34 operative procedures: 16 orthopaedic, six neurosurgical, four laparotomies and eight wound debridement and closure. Eighty-one percent of the patients received ventilatory support and nine patients (14%) died, all from brain injuries. Pedestrian injury is an important child health problem in New Zealand and studies aimed at the identification of factors that place children at risk for these injuries are needed.

Accidents, Traffic↗
PubMed1990

T cell receptor-bearing cells among rat intestinal intraepithelial lymphocytes are mainly alpha/beta+ and are thymus dependent.

Rearrangement of both the beta and gamma chain T cell receptor (TcR) genes was detected in intestinal intraepithelial lymphocytes (IEL) from normal euthymic rats. Flow cytometric analyses showed that about 73% of the IEL were CD3+ (1F4) and that 67% were TcR alpha/beta+ (R73). About 5% of the IEL were found to be CD3+, TcR alpha/beta- in double-labeling experiments suggesting that a small fraction of IEL in the rat express the alternative TcR gamma/delta. More than 70% of the IEL were granular implying that many CD3+ IEL are granular. In IEL from athymic nude rats no rearrangement of either the TcR beta or gamma chain genes or surface expression of CD3 or TcR alpha/beta was detected despite the fact that about 95% of the cells were granular and morphologically similar to those in normal rats. Taken together our data suggest that the majority of IEL in the rat express the conventional TcR alpha/beta and that TcR-bearing cells in the gut epithelium are thymus dependent.

Animals↗
PubMed1990

Expression of the Escherichia coli K5 capsular antigen: immunoelectron microscopic and biochemical studies with recombinant E. coli.

The capsular K5 polysaccharide, a representative of group II capsular antigens of Escherichia coli, has been cloned previously, and three gene regions responsible for polymerization and surface expression have been defined (I. S. Roberts, R. Mountford, R. Hodge, K. B. Jann, and G. J. Boulnois, J. Bacteriol. 170:1305-1310, 1988). In this report, we describe the immunoelectron microscopic analysis of recombinant bacteria expressing the K5 antigen and of mutants defective in either region 1 or region 3 gene functions, as well as the biochemical analysis of the K5 capsular polysaccharide. Whereas the K5 clone expressed the K5 polysaccharide as a well-developed capsule in about 25% of its population, no capsule was observed in whole mount preparations and ultrathin sections of the expression mutants. Immunogold labeling of sections from the region 3 mutant revealed the capsular K5 polysaccharide in the cytoplasm. With the region 1 mutant, the capsular polysaccharide appeared associated with the cell membrane, and, unlike the region 3 mutant polysaccharide, the capsular polysaccharide could be detected in the periplasm after plasmolysis of the bacteria. Polysaccharides were isolated from the homogenized mutants with cetyltrimethylammonium bromide. The polysaccharide from the region 1 mutant had the same size as that isolated from the capsule of the original K5 clone, and both polysaccharides were substituted with phosphatidic acid. The polysaccharide from the region 3 mutant was smaller and was not substituted with phosphatidic acid. These results prompt us to postulate that gene region 3 products are involved in the translocation of the capsular polysaccharide across the cytoplasmic membrane and that region 1 directs the transport of the lipid-substituted capsular polysaccharide through the periplasm and across the outer membrane.

Antibodies, Monoclonal↗
PubMed1989

Activity of CMP-2-keto-3-deoxyoctulosonic acid synthetase in Escherichia coli strains expressing the capsular K5 polysaccharide implication for K5 polysaccharide biosynthesis.

The activity of the cytoplasmic CMP-2-keto-3-deoxyoctulosonic acid synthetase (CMP-KDO synthetase), which is low in Escherichia coli rough strains such as E. coli K-12 and in uncapsulated strains such as E. coli O111, was significantly elevated in encapsulated E. coli O10:K5 and O18:K5. This enzyme activity was even higher in an E. coli clone expressing the K5 capsule. This and the following findings suggest a correlation between elevated CMP-KDO synthetase activity and the biosynthesis of the capsular K5 polysaccharide. (i) Expression of the K5 polysaccharide and elevated CMP-KDO synthetase activity were observed with bacteria grown at 37 degrees C but not with cells grown at 20 degrees C or below. (ii) The recovery kinetics of capsule expression of intact bacteria, in vitro K5 polysaccharide-synthesizing activity of bacteria, and CMP-KDO synthetase activity of bacteria after temperature upshift from 18 to 37 degrees C were the same. (iii) Chemicals which inhibit capsule (polysaccharide) expression also inhibited the elevation of CMP-KDO synthetase activity. The chromosomal location of the gene responsible for the elevation of this enzyme activity was narrowed down to the distal segment of the transport region of the K5 expression genes.

Cloning, Molecular↗
PubMed1989

Acute effects of progesterone and the antiprogestin RU 486 on gonadotropin secretion in the follicular phase of the menstrual cycle.

Considerable controversy still exists concerning the role of progesterone in the initiation of the midcycle gonadotropin surge in humans. We, therefore, carried out a prospective randomized study to determine the potential of progesterone to initiate a gonadotropin surge and the acute effects of a potent progesterone antagonist (RU 486) on follicular phase gonadotropin secretion in normal women. The women underwent frequent blood sampling for 4 in the midfollicular (day 6) or late follicular phase (day 10). They then received either progesterone (10 mg, im) or RU 486 (10 or 100 mg, orally), and blood sampling was continued for an additional 8 h. Four women received each of the drug regimens in the early follicular phase, and four received each regimen in the late follicular phase. Two additional women were studied as control subjects at each stage of the cycle. Progesterone administration in the mid- and late follicular phases resulted in an acute increase in plasma LH and FSH concentrations, and the increases correlated with the base line plasma estradiol concentrations (P less than 0.05). In contrast to progesterone, the women who received RU 486 in the mid- and late follicular phases had a reduction in plasma LH and FSH concentrations after drug administration. The response in the mid-follicular phase was considerably less than that in the late follicular phase, and the extent of the response correlated with the baseline plasma estradiol concentrations (P less than 0.005). The changes were similar in response to both RU 486 doses. We conclude that progesterone can initiate a gonadotropin surge in the late follicular phase of the menstrual cycle. The inhibitory effect of the progesterone antagonist RU 486 suggests that a positive feedback mechanism involving progesterone may be influential some time before the surge onset.

Adult↗