Search PubMed⌕ Search

Biomedical subjects

R J Roberts

Publications and source records attributed to R J Roberts.

At least 145 records · Page 8Linked to original sources
PubMed1989

Cloning and characterization of the genes encoding the MspI restriction modification system.

The genes encoding the MspI restriction modification system, which recognizes the sequence 5' CCGG, have been cloned into pUC9. Selection was based on expression of the cloned methylase gene which renders plasmid DNA insensitive to MspI cleavage in vitro. Initially, an insert of 15 kb was obtained which, upon subcloning, yielded a 3 kb EcoRI to HindIII insert, carrying the genes for both the methylase and the restriction enzyme. This insert has been sequenced. Based upon the sequence, together with appropriate subclones, it is shown that the two genes are transcribed divergently with the methylase gene encoding a polypeptide of 418 amino acids, while the restriction enzyme is composed of 262 amino acids. Comparison of the sequence of the MspI methylase with other cytosine methylases shows a striking degree of similarity. Especially noteworthy is the high degree of similarity with the HhaI and EcoRII methylases.

Amino Acid Sequence↗
PubMed1989

Predictive motifs derived from cytosine methyltransferases.

Thirteen bacterial DNA methyltransferases that catalyze the formation of 5-methylcytosine within specific DNA sequences possess related structures. Similar building blocks (motifs), containing invariant positions, can be found in the same order in all thirteen sequences. Five of these blocks are highly conserved while a further five contain weaker similarities. One block, which has the most invariant residues, contains the proline-cysteine dipeptide of the proposed catalytic site. A region in the second half of each sequence is unusually variable both in length and sequence composition. Those methyltransferases that exhibit significant homology in this region share common specificity in DNA recognition. The five highly conserved motifs can be used to discriminate the known 5-methylcytosine forming methyltransferases from all other methyltransferases of known sequence, and from all other identified proteins in the PIR, GenBank and EMBL databases. These five motifs occur in a mammalian methyltransferase responsible for the formation of 5-methylcytosine within CG dinucleotides. By searching the unidentified open reading frames present in the GenBank and EMBL databases, two potential 5-methylcytosine forming methyltransferases have been found.

Amino Acid Sequence↗
PubMed1989

Influence of absorbable and nonabsorbable lipids and lipidlike substances on drug bioavailability.

The influence of three diets (olestra, triglyceride oil, and water) on the bioavailability of a single dose of propranolol, diazepam, norethindrone, and ethinyl estradiol was evaluated. For each drug the diets were randomly administered in a crossover fashion; a period of at least 14 days separated each of the drug studies. Blood samples were obtained before and after the oral administration of test drug and diet. Specific timing of blood samples varied for the respective drugs. AUCs were determined by the trapezoidal method. There were no statistical differences observed in the absorption of the various drugs evaluated in this study when administered with olestra, triglyceride oil, or water, except that the time to peak concentration of diazepam was significantly longer with the triglyceride oil than with olestra or water.

Adult↗
PubMed1989

Tinker toy test performance and vocational outcome in patients with closed-head injuries.

Fifty patients who had suffered closed-head injury with no resultant physical disabilities and 25 normal controls were administered a modified version of Lezak's Tinker Toy Test. All head-injured patients were examined at least 24 months following medical clearance to return to work. Twenty-five of the head injured had been unable to return to work or sustain normal competitive employment as a result of their head injuries. The remaining 25 had returned to their previous jobs successfully or had been employed for at least 6 months prior to assessment. Whereas all but one of the head injured who returned to work scored normally on the Tinker Toy Test, nearly half of the nonreturnees performed below the level of the worst control.

Adult↗
PubMed1989

Multiple splicing factors are released from endogenous complexes during in vitro pre-mRNA splicing.

Pre-mRNA splicing occurs in a macromolecular complex called the spliceosome. Efforts to isolate spliceosomes from in vitro splicing reactions have been hampered by the presence of endogenous complexes that copurify with de novo spliceosomes formed on added pre-mRNA. We have found that removal of these large complexes from nuclear extracts prevents the splicing of exogenously added pre-mRNA. We therefore examined these complexes for the presence of splicing factors and proteins known or thought to be involved in RNA splicing. These fast-sedimenting structures were found to contain multiple small nuclear ribonucleoproteins (snRNPs) and a fragmented heterogeneous nuclear ribonucleoprotein complex. At least two splicing factors other than the snRNPs were also associated with these large structures. Upon incubation with ATP, these splicing factors as well as U1 and U2 snRNPs were released from these complexes. The presence of multiple splicing factors suggests that these complexes may be endogenous spliceosomes released from nuclei during preparation of splicing extracts. The removal of these structures from extracts that had been preincubated with ATP yielded a splicing extract devoid of large structures. This extract should prove useful in the fractionation of splicing factors and the isolation of native spliceosomes formed on exogenously added pre-mRNA.

Cell Fractionation↗
PubMed1989

Passenger fear of flying: behavioural treatment with extensive in-vivo exposure and group support.

The techniques used in the treatment of passenger fear of flying are described. They include behaviour modification techniques (relaxation, systematic desensitization, and cognitive restructuring), an educational programme, high in-vivo exposure, and group support. Results from self-rating scales and qualitative feedback from course participants during 1979-1985, show that the collective use of these techniques contribute significantly to a reduction of fear and discomfort associated with passenger flying.

Aerospace Medicine↗
PubMed1988

Sequence motifs specific for cytosine methyltransferases.

Using a new alignment method, the sequences of 13 m5C methyltransferases (MTases) have been examined. Five extremely well-conserved blocks of sequence have been detected and have been used as fixed points for the alignment of the 13 sequences. Following this initial alignment, five further blocks of similarity have been identified to give a total of ten recognizable blocks of sequence homology that are all arranged in a common order. The structures of these MTases consist of a variable-length N-terminal arm followed by eight well-conserved blocks each separated by small variable-length regions. A large variable-length segment of 90 to 270 amino acids (aa) then follows. After this are two blocks, and a variable-length C-terminal segment completes the sequence. Within the final alignment, 20 aa in the protein sequences, and 86 nucleotides in the nucleotide sequences are invariant. The strongest conservation is found in proximity to a suspected functional site that contains the dipeptide proline-cysteine. Consensus patterns can be defined for the five best conserved blocks and, when used as search motifs, are able to clearly distinguish between the m5C MTases and all other identified proteins in the PIR database. This suggests they may be of use in identifying putative MTases among protein sequences of unknown function.

Amino Acid Sequence↗
PubMed1988

Port Pirie Cohort Study: environmental exposure to lead and children's abilities at the age of four years.

We studied the effect of environmental exposure to lead on children's abilities at the age of four years in a cohort of 537 children born during 1979 to 1982 to women living in a community situated near a lead smelter. Samples for measuring blood lead levels were obtained from the mothers antenatally, at delivery from the mothers and umbilical cords, and at the ages of 6, 15, and 24 months and then annually from the children. Concurrently, the mothers were interviewed about personal, family, medical, and environmental factors. Maternal intelligence, the home environment, and the children's mental development (as evaluated with use of the McCarthy Scales of Children's Abilities) were formally assessed. The mean blood lead concentration varied from 0.44 mumol per liter in midpregnancy to a peak of 1.03 mumol per liter at the age of two years. The blood lead concentration at each age, particularly at two and three years, and the integrated postnatal average concentration were inversely related to development at the age of four. Multivariate analysis incorporating many factors in the children's lives indicated that the subjects with an average postnatal blood lead concentration of 1.50 mumol per liter had a general cognitive score 7.2 points lower (95 percent confidence interval, 0.3 to 13.2; mean score, 107.1) than those with an average concentration of 0.50 mumol per liter. Similar deficits occurred in the perceptual-performance and memory scores. Within the range of exposure studied, no threshold dose for an effect of lead was evident. We conclude that postnatal blood lead concentration is inversely related to cognitive development in children, although one must be circumspect in making causal inferences from studies of this relation, because of the difficulties in defining and controlling confounding effects.

Australia↗
PubMed1988

Neuropsychological performance in lateralized parkinsonism.

Seven dextral patients with Parkinson's disease (PD) who had predominant right-sided motor signs were compared on neuropsychological tests with eight dextral patients with PD who had predominant left-sided signs. Objective criteria for group designation were developed from clinical ratings. The patient subgroups were matched on age, education, estimated premorbid IQ, severity of motor signs, and medication usage. Patients with signs lateralized to the right were more impaired on tests of dominant hemisphere function (serial digit learning, confrontation naming, and verbal associative fluency), but no differences were found on tests of nondominant hemisphere function (form sequence learning, line orientation, facial recognition), indicating some correlation of neuropsychological performance with lateralization of predominant motor signs. Findings demonstrate that the cognitive deficits (particularly visuospatial) previously reported in the literature are not seen consistently in all subjects with PD.

Depression↗
PubMed1988

Port Pirie Cohort study: childhood blood lead and neuropsychological development at age two years.

The Port Pirie Cohort Study is an ongoing prospective study of the relationship between exposure to environmental lead within a lead smelter community, and neuropsychological development in early childhood. Over 600 children, originally recruited during antenatal life, underwent serial blood lead estimations up to two years of age. Systematic interview information was collected on a range of variables, and formal developmental assessment (Bayley Scales of Infant Development) was carried out at 24 months of age. Blood lead concentrations measured antenatally (maternal), at delivery (maternal and umbilical cord) and postnatally at 6, 15 and 24 months were negatively correlated (p less than 0.05) with mental development at 24 months of age. Geometric mean blood lead concentrations (microgram/dl) were 14.3, 20.8 and 21.2 at 6, 15 and 24 months of age respectively. When multiple covariates, including maternal IQ, were controlled for in multiple regression analysis, a statistically significant (p less than 0.01) inverse association was observed between blood lead concentration (PbB) measured at 6 months of age and mental development at 2 years of age. No such association was evident for psychomotor development. When the quality of the home environment (HOME Score) was added to the multiple regression model, the inverse association between blood lead concentration at 6 months of age and mental development at 2 years persisted, albeit less strongly (p = 0.07). From this analysis, it is estimated that a child with with PbB of 30 micrograms/dl at age 6 months will have a deficit of 3.3 points (approximately 3%) on the Bayley Mental Development Scale relative to a child with PbB of 10 micrograms/dl.

Child Development↗
PubMed1988

Influence of physical characteristics of intravenous systems on drug delivery.

The influence of multiple intravenous system factors on the time required to deliver a drug dose was evaluated in vitro using a factorial study design. The study factors included (1) 5 intraluminal tubing diameters, (2) 2 intravenous tubing positions, (3) 2 intravenous infusion rates, and (4) 2 intravenous tubing lengths. For each intravenous system that represented the respective combination of study factors, a 1-ml dose of 14C-labeled potassium penicillin G was administered and the effusate was collected over time. A liquid scintillation technique was used to quantitate the amount of drug delivered. In-line pressures that resulted from the experimental conditions were measured in order to examine for correlations between in-line pressure and alterations in drug delivery time. Analysis of variance and stepwise procedures were used to determine significance of these factors on drug delivery time. It was determined that complex fluid dynamics resulting from the combined influences of tubing diameter, tubing length and infusion rate appears to have a significant influence on drug delivery time. It is important to use efficient intravenous systems for intravenous therapy in order to predict and control intravenous drug delivery.

Drug Administration Schedule↗
PubMed1988

Enteral drug administration practices: report of a preliminary survey.

This study was initiated to determine whether there is sufficient variation in enteral drug administration practices in hospitalized pediatric patients to result in adverse therapeutic consequences. A survey was developed and administered to nurses from three pediatric and six general hospitals. A total of 317 pediatric nurses responded. Results of the survey confirmed that the primary responsibility for administering enteral medications resides with the nurse. It also documented that many elements in the administration of enteral medications vary significantly among nurses, although nursing personnel expressed confidence in the efficacy of their individual drug administration techniques. Further quantitative evaluations of the efficacy of practices of enteral drug administration must be performed before meaningful standardization of drug administration techniques can be accomplished.

Administration, Oral↗
PubMed1987

In vitro formation of a lariat structure containing a G2'-5'G linkage.

We have examined the effects of base changes at the lariat branch site of a modified adenovirus major late precursor mRNA (pre-mRNA). Replacement of the A residue at the lariat attachment site with a G residue was studied. Incubation of this altered pre-mRNA with nuclear extracts of HeLa cells yielded less spliced mRNA (10-fold) than similar reactions with the wild type pre-mRNA. The intron lariat formed during the reaction with the mutant transcript contained the predominant branch (2'-5' phosphodiester linkage) to an upstream A residue. In contrast, the intron/exon 2 lariat contained the predominant branch to the substituted G residue. These results indicated that detectable spliced RNA was formed when the lariat was attached at the A residue but not when the lariat was attached to the substituted G residue. A second mutation was introduced into the transcript by substituting an additional G residue at the alternative A branch site. When transcript derived from this plasmid was incubated with nuclear extract, cleavage occurred at the 5' splice site, and an intron/exon 2 lariat was produced, but spliced RNA was not detected. T1 RNase digestion and primer extension analyses of this intron/exon 2 lariat revealed that all of the lariat formed on the G residue at the normal attachment site.

Adenoviridae↗