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Biomedical subjects

R J Roberts

Publications and source records attributed to R J Roberts.

At least 91 records · Page 5Linked to original sources
PubMed1995

Nitric oxide-induced cytotoxicity: involvement of cellular resistance to oxidative stress and the role of glutathione in protection.

A series of experiments were designed to examine the potential cytotoxicity of nitric oxide (NO), or reactive species derived from NO, in HA1 fibroblasts and H2O2-resistant variants of this cell line, designated OC14 cells. A 1-h exposure at 37 degrees C to a 1.7 mM bolus dose of NO, prepared in N2-gassed medium, significantly reduced clonogenic survival in the HA1 fibroblasts line to 60% of control cells treated with N2-gassed medium alone. The OC14 cells were found to be completely resistant (100% survival) to NO-mediated injury in comparable experiments. A second set of experiments was designed to determine the role of the intracellular antioxidant, glutathione, in protection against NO-mediated injury. Depletion of total glutathione resulted in a significant reduction in HA1 and OC14 clonogenic survival to 8% and 50% when compared with respective control cells. The effect of total glutathione depletion on NO-initiated toxicity in HA1 cells was dose- and cell-density dependent and was observed to occur within 5 min of exposure to NO. Further evidence of cytotoxicity was demonstrated by loss of trypan blue dye exclusion properties in glutathione-depleted HA1 cells after NO exposure. Other experiments demonstrated that nitrate and nitrite exposure produced no cytotoxicity in glutathione-depleted HA1 cells and that coincubation of NO-saturated medium with oxyhemoglobin inhibited NO-induced cytotoxicity in glutathione-depleted HA1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Characteristics and mechanisms of epilepsy spectrum disorder: an explanatory model.

Recently, a complex neurobehavioral disorder with paroxysmal affective, psychosensory, and cognitive symptoms has been described by a number of different neuropsychiatric and neuropsychological practitioners. Although a variety of different terms have been used to characterize this clinical entity, the recently coined term epilepsy spectrum disorder (ESD) will be used for the purposes of this article. The clinical identification, neuropsychological characteristics, differential diagnosis, etiology, and treatment response of such patients will be reviewed. The possible neuropathological and neurophysiological mechanisms underlying ESD and implications for future research will also be discussed It is argued that neuropsychologists should be more familiar with this syndrome because such patients are frequently referred for neuropsychological assessment when practitioners from medical disciplines are confused by the atypical and polysymptomatic clinical presentations of ESD patients.

Journal Article↗
PubMed1994

Organization and sequence of the HpaII restriction-modification system and adjacent genes.

We report the organization of the HpaII restriction and modification (R-M) system from Haemophilus parainfluenzae (recognition sequence: 5'...CCGG...3'), the sequence of the gene coding for the HpaII restriction endonuclease, and the sequence of the upstream flanking DNA. The HpaII system comprises two genes, hpaIIM, coding for the methyltransferase (MTase; 358 amino acids (aa), 40.4 kDa: product, Cm5CGG), and hpaIIR, coding for the restriction endonuclease (ENase; 358 aa, 40.9 kDa: product, C'CGG). The genes are adjacent, they have the same orientation, and they occur in the order hpaIIM then hpaIIR. The ENase bears little as sequence similarity to the isoschizomeric R.BsuFI and R.MspI ENases. Upstream of, and partly overlapping hpaIIM is the coding sequence for a 141-aa protein that resembles the very-short-patch-repair endonuclease (Vsr) of Escherichia coli. Upstream of that is the coding sequence for a protein that resembles valyl-tRNA synthetase (ValS).

Amino Acid Sequence↗
PubMed1994

HhaI methyltransferase flips its target base out of the DNA helix.

The crystal structure has been determined at 2.8 A resolution for a chemically-trapped covalent reaction intermediate between the HhaI DNA cytosine-5-methyltransferase, S-adenosyl-L-homocysteine, and a duplex 13-mer DNA oligonucleotide containing methylated 5-fluorocytosine at its target. The DNA is located in a cleft between the two domains of the protein and has the characteristic conformation of B-form DNA, except for a disrupted G-C base pair that contains the target cytosine. The cytosine residue has swung completely out of the DNA helix and is positioned in the active site, which itself has undergone a large conformational change. The DNA is contacted from both the major and the minor grooves, but almost all base-specific interactions between the enzyme and the recognition bases occur in the major groove, through two glycine-rich loops from the small domain. The structure suggests how the active nucleophile reaches its target, directly supports the proposed mechanism for cytosine-5 DNA methylation, and illustrates a novel mode of sequence-specific DNA recognition.

5-Methylcytosine↗
PubMed1994

The DNA (cytosine-5) methyltransferases.

The m5C-MTases form a closely-knit family of enzymes in which common amino acid sequence motifs almost certainly translate into common structural and functional elements. These common elements are located predominantly in a single structural domain that performs the chemistry of the reaction. Sequence-specific DNA recognition is accomplished by a separate domain that contains recognition elements not seen in other structures. This, combined with the novel and unexpected mechanistic feature of trapping a base out of the DNA helix, makes the m5C-MTases an intriguing class of enzymes for further study. The reaction pathway has suddenly become more complicated because of the base-flipping and much remains to be learned about the DNA recognition elements in the family members for which structural information is not yet available.

Amino Acid Sequence↗
PubMed1994

Issues and problems associated with drug delivery in pediatric patients.

Inherent problems exist in the actual delivery of doses of medications to pediatric patients, particularly with the i.v. route of drug administration. Standardized policies and procedures for recognized problems with specific routes of drug administration, along with pharmaceutical industry cooperation, are essential for solving drug delivery problems in pediatric therapeutics.

Adult↗
PubMed1994

Do dichotic word listening asymmetries predict side of temporal lobe seizure onset?

Dichotic word listening asymmetries are thought to be useful in predicting side of temporal lobe dysfunction. However, little direct evidence exists to support this assumption in practice, especially in patients with subtle epileptogenic lesions. To determine if word listening ear asymmetries are valid predictors of side of temporal lobe seizure onset, we examined the preoperative dichotic word listening performance of 80 patients with either left (N = 41) or right (N = 39) temporal lobe (TL) seizure foci. On a group level, patients showed a statistically significant 'lesion effect' as evidenced by a relative deficit in the ear contralateral to the side of lesion. Prediction of side of seizure focus in individual cases, however, was poor: depending upon the criteria used, 61% to 80% of epileptics with unilateral temporal lobe foci did not show the expected contralateral ear deficit. Results suggest that caution be exercised when inferring side of temporal lobe seizure focus through dichotic word listening asymmetries in individual temporal lobe epilepsy cases.

Adult↗
PubMed1994

Yet another short-form of the Wechsler scales for use in neuropsychological assessment.

The general purpose of the present study was to make Hamsher's seven subtest short-form of the WAIS-R (or WAIS) more accessible to neuropsychologists. Formulas are presented for both instruments which permit calculation of Verbal-Conceptual, Attention-Concentration, Perceptual-Organizational, and Full Scale deviation quotients. Results from two samples of psychiatric patients suggest that this abbreviated approach to using the Wechsler IQ batteries provides reasonably accurate estimates of traditional IQ scores. A case example illustrates how analysis of the various deviation quotients can contribute to neuropsychological reasoning at the level of the individual patient.

Journal Article↗
PubMed1994

The Dichotic Word Listening Test: preliminary observations in American and Canadian samples.

The present article describes observations of 670 American and Canadian child and adult control subjects on the recently developed Dichotic Word Listening Test (DWLT). The task was also administered to a sample of American children with traumatic brain injuries (n=21) of varying severity and a sample of American adults with mild traumatic injuries (n=36). The conceptual focus in this line of research was on using normative observations to identify clinically defective channels of auditory processing among patients. The principal findings were as follow: 1) the DWLT was sensitive to the effects of cerebral dysfunction following traumatic brain injury; 2) differences among normal samples with different demographic backgrounds were frequently observed, arguing for the development of local norms; 3) a shorter form of the DWLT task (DWLT30) can be used for screening purposes with relatively little reduction in sensitivity to cerebral dysfunction; 4) there appeared to be considerable improvement of DWLT performance between the ages of five and seven, due largely to higher scores from the left auditory channel; and 5) there were indications that use of French (rather than English) as one's native language before age six can negatively influence performance in adulthood on an English version of the DWLT. In general, the present findings suggest that the DWLT is likely to have relatively broad applicability for neuropsychological assessment across the life-span.

Journal Article↗
PubMed1994

VISA: Visual Sequence Analysis for the comparison of multiple amino acid sequences.

VISA (VIsual Sequence Analysis) is a software package that displays global similarities within a set of related protein sequences. The program identifies amino acid patterns that are common to many members of the set of sequences and displays them as a series of histograms. Individual peaks on the display can be assigned a color and analogous peaks in the other sequences are then automatically marked in the same color. This can be repeated for each significant peak and leads to a display in which major matching segments of multiple amino acid sequences appear as dominant peaks of the histograms with matching colors. These peaks usually correspond to the conserved sequence motifs that are characteristic of particular proteins. An extensive set of software tools is included to help the localization, visualization and analysis of the global similarities displayed. VISA provides a graphic overview of the sequence similarity that can help to understand the architecture of the protein family and can be helpful while designing experiments to probe function.

Algorithms↗
PubMed1994

REBASE--restriction enzymes and methylases.

REBASE is a comprehensive database of information about restriction enzymes and their associated methylases, including their recognition and cleavage sites and their commercial availability. Information from REBASE is available via monthly electronic mailings as well as via WAIS and anonymous ftp. Specialized files are available that can be used directly by many software packages.

Base Sequence↗
PubMed1994

Long-term neuropsychological sequelae of fever associated with amnesia.

It has been well established that high fever can cause substantial damage to the cerebellum and also cause multiple small vascular lesions in neocortex and subcortical white matter. Beyond acute effects, the neuropsychological sequelae of these latter cortical and subcortical lesions have not been studied. The investigation reported involved 36 VA patients with a history of serious febrile illness. The febrile illnesses of the pyrexic subjects did not cause febrile seizures and resulted from diseases that did not directly involve the brain (e.g., encephalitis, meningitis, malaria). Control subjects were combat veterans who had suffered gunshot wounds, but who had no history of febrile illness. Pyrexic patients performed worse than controls on a variety of measures including language, memory, concentration, and word finding as well as failing a test of dichotic listening for words. Results demonstrate that hyperpyrexia can have lasting neuropsychological sequelae, and suggest that history of serious febrile illness be considered as an exclusionary criterion for participation in neuropsychological research concerning other topics or disorders.

Journal Article↗
PubMed1993

Crystal structure of the HhaI DNA methyltransferase complexed with S-adenosyl-L-methionine.

The first three-dimensional structure of a DNA methyltransferase is presented. The crystal structure of the DNA (cytosine-5)-methyltransferase, M.HhaI (recognition sequence: GCGC), complexed with S-adenosyl-L-methionine has been determined and refined at 2.5 A resolution. The core of the structure is dominated by sequence motifs conserved among all DNA (cytosine-5)-methyltransferases, and these are responsible for cofactor binding and methyltransferase function.

Amino Acid Sequence↗
PubMed1993

The DNA binding affinity of HhaI methylase is increased by a single amino acid substitution in the catalytic center.

The HhaI methyltransferase recognizes the sequence GCGC and transfers a methyl group to C5 of the first cytosine residue. All m5C-methyltransferases contain a highly conserved sequence motif called the P-C motif. The cysteine residue of this motif is involved in catalysis by forming a covalent bond with the 6-position of cytosine prior to methyl group transfer. For the EcoRII methyltransferase, it has been shown that substitution of this catalytic cysteine by glycine is cytotoxic to E.coli cells expressing the mutant methyltransferase (Wyszynski et al. Nucl. Acids Res. 20: 319, 1992). We now show that this observation can be extended to the HhaI system and suggest that the cytotoxicity is due to abnormally tight DNA binding by the mutant methyltransferase, which probably interferes with replication or transcription.

Amino Acid Sequence↗