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Biomedical subjects

L Snyder

Publications and source records attributed to L Snyder.

At least 37 records · Page 2Linked to original sources
PubMed1998

Specific peptide-activated proteolytic cleavage of Escherichia coli elongation factor Tu.

Phage exclusion is a form of programmed cell death in prokaryotes in which death is triggered by infection with phage, a seemingly altruistic response that limits multiplication of the phage and its spread through the population. One of the best-characterized examples of phage exclusion is the exclusion of T-even phages such as T4 by the e14-encoded Lit protein in many Escherichia coli K-12 strains. In this exclusion system, transcription and translation of a short region of the major head coat protein gene late in phage infection activates proteolysis of translation elongation factor Tu (EF-Tu), blocking translation and multiplication of the phage. The cleavage occurs between Gly-59 and Ile-60 in the nucleotide-binding domain. In the present work, we show that a 29-residue synthetic peptide spanning the activating region of the major head coat protein can activate the cleavage of GDP-bound EF-Tu in a purified system containing only purified EF-Tu and purified Lit protein. Lit behaves as a bona fide enzyme in this system, cleaving EF-Tu to completion when present at substoichiometric amounts. Two mutant peptides with amino acid changes that reduce the activation of cleavage of EF-Tu in vivo were also greatly reduced in their ability to activate EF-Tu cleavage in vitro but were still able to activate cleavage at a high concentration. Elongation factor G, which has the same sequence at the cleavage site and a nucleotide-binding domain similar to EF-Tu, was not cleaved by this system, and neither was heat-inactivated EF-Tu, suggesting that the structural context of the cleavage site may be important for specificity. This system apparently represents an activation mechanism for proteolysis that targets one of nature's most evolutionarily conserved proteins for site-specific cleavage.

Amino Acid Sequence↗
PubMed1998

'Twas the night."

Explore the source record for details and available documents.

Journal Article↗
PubMed1997

Bone mineral density and survival of elements and element portions in the bones of the Crow Creek massacre victims.

The interpretation of archaeologically-derived skeletal series is dependent on the elements and portions of elements preserved for examination. Bone and bone portion survival is affected by factors, both intrinsic and extrinsic to the elements themselves, that influence deterioration and preservation. Among the intrinsic variables, the density of the element and element portion are particularly important with respect to the degree of preservation. Recently reported bone mineral density values from a contemporary human sample are compared to the survival of prehistoric limb bones of the Crow Creek specimens, a fourteenth-century massacre skeletal series. The contemporary density values are positively correlated with Crow Creek element and element portion survival. Two calculations of bone mineral density, however, are more closely related to preservation than a third. Such density information has implications for assessing minimum number of elements and individuals and documenting taphonomic processes.

Adolescent↗
PubMed1996

Ethical and legal issues in nursing home care.

Physicians who provide care for nursing home residents are regularly challenged by ethical and legal issues. Because nursing home care is complicated by numerous regulations and because nursing home residents have complex medical and social problems, some issues are unique to the long-term care setting and others present in unfamiliar ways. Some issues frequently encountered in this context are discussed: advance directives, competence and decision-making capacity, decisions about life-sustaining treatment, resident abuse, restraints, psychotropic medications, risk management, participation in research, and ethics committees. With knowledge of the legal and ethical framework and understanding of some of the common, complicated issues that arise, physicians should be better equipped to provide optimal care for nursing home residents.

Advance Care Planning↗
PubMed1996

Promoter mapping of the mouse Tcp-10bt gene in transgenic mice identifies essential male germ cell regulatory sequences.

Transgenic mice were generated to localize essential promoter elements in the mouse testis-expressed Tcp-10 genes. These genes are expressed exclusively in male germ cells, and exhibit a diffuse range of transcriptional start sites, possibly due to the absence of a TATA box. A series of transgene constructs containing different amounts of 5' flanking DNA revealed that all sequences necessary for appropriate temporal and tissue-specific transcription of Tcp-10 reside between positions -1 to -973. All transgenic animals containing these sequences expressed a chimeric transgene at high levels, in a pattern that paralleled the endogenous genes. These experiments further defined a 227 bp fragment from -746 to -973 that was absolutely essential for expression. In a gel-shift assay, this 227-bp fragment bound nuclear protein from testis, but not other tissues, to yield two retarded bands. Sequence analysis of this fragment revealed a half-site for the AP-2 transcription factor recognition sequence. Gel shift assays using native or mutant oligonucleotides demonstrated that the putative AP-2 recognition sequence was essential for generating the retarded bands. Since the binding activity is testis-specific, but AP-2 expression is not exclusive to male germ cells, it is possible that transcription of Tcp-10 requires interaction between AP-2 and a germ cell-specific transcription factor.

Animals↗
PubMed1996

Narrative elaboration: test of a new procedure for interviewing children.

Because young children provide incomplete accounts of the past and tend to acquiesce to leading questions, procedures are needed to help them describe past events fully, without contaminating memory. This study tests the efficacy of "narrative elaboration," an innovative procedure designed to expand children's spontaneous reports of past events, reducing the need for leading questions. One hundred thirty-two children from 2 age groups (7-8 years and 10-11 years) were assigned randomly to 1 of 3 preparation conditions: (a) narrative elaboration intervention, (b) instruction-based intervention, and (c) control group. After participating in a staged activity and subsequent preparation sessions, children were interviewed about the activity. Children in the narrative elaboration condition demonstrated a 53% improvement in spontaneous recall over the control group, without compromising accuracy. Younger children using the narrative elaboration procedure performed at the level of older children in the control group. Discussion centers on implications for interviewing child witnesses and preparing them for courtroom examination.

Age Factors↗
PubMed1995

Phage T4-coded Stp: double-edged effector of coupled DNA and tRNA-restriction systems.

The optional Escherichia coli prr locus encodes two physically associated restriction systems: the type IC DNA restriction-modification enzyme EcoprrI and the tRNA(Lys)-specific anticodon nuclease, specified by the PrrC polypeptide. Anticodon nuclease is kept latent as a result of this interaction. The activation of anticodon nuclease, upon infection by phage T4, may cause depletion of tRNA(Lys) and, consequently, abolition of T4 protein synthesis. However, this effect is counteracted by the repair of tRNA(Lys) in consecutive reactions catalysed by the phage enzymes polynucleotide kinase and RNA ligase. Stp, a short polypeptide encoded by phage T4, has been implicated with activation of the anticodon nuclease. Here we confirm this notion and also demonstrate a second function of Stp: inhibition of EcoprrI restriction. Both effects depend, in general, on the same residues within the N-proximal 18 residue region of Stp. We propose that Stp alters the conformation of EcoprrI and, consequently, of PrrC, allowing activation of the latent anticodon nuclease. Presumably, Stp evolved to offset a DNA restriction system of the host cell but was turned, eventually, against the phage as an activator of the appended tRNA restriction enzyme.

Amino Acid Sequence↗
PubMed1995

Thoracoscopic plication of the diaphragm.

Plication of the diaphragm in symptomatic patients with phrenic nerve paralysis provides excellent relief of excertional dyspnea and significantly increases arterial oxygen tension, and all lung volumes except residual volume. We report diaphragmatic plication using the minimally invasive technique of VATS. This procedure provides excellent relief of symptoms with minimal morbidity and short hospitalization.

Aged↗
PubMed1995

Supportive seminar groups: an intervention for early stage dementia patients.

A supportive seminar group was developed and conducted for individuals with early stage dementia and their caregivers. The eight sessions focused on pertinent topics, namely, coping with memory problems, daily living, self-esteem, relationships, health, legal, and financial concerns. Content analysis of the evaluative statements from nine men and six women patients revealed positive themes of feelings of purposefulness, gratification, belongingness, and survival, while other themes reflected the turmoil of the disease, namely, feelings of helplessness, devaluation, and unpredictability. These preliminary findings lend support to the feasibility of a group approach for early stage dementia patients.

Alzheimer Disease↗
PubMed1995

Phage-exclusion enzymes: a bonanza of biochemical and cell biology reagents?

Many parasitic DNA elements including prophages and plasmids synthesize proteins that kill the cell after infection by other phages, thereby blocking the multiplication of the infecting phages and their spread to other nearby cells. The only known function of these proteins is to exclude the infecting phage, and therefore to protect their hosts, and thereby the DNA elements themselves, against phage contagion. Many of these exclusions have been studied extensively and some have long been used in molecular genetics, but their molecular basis was unknown. The most famous of the phage exclusions are those caused by the Rex proteins of lambda prophage. The Rex exclusions are still not completely understood, but recent evidence has begun to lead to more specific models for their action. One of the Rex proteins, RexA, may be activated by a DNA-protein complex, perhaps a recombination or replication intermediate, produced after phage infection. In the activated state, RexA may activate RexB, which has been proposed to be a membrane ion channel that allows the passage of monovalent cations, destroying the cellular membrane potential, and killing the cell. We now understand two other phage exclusions at the molecular level which use strategies that are remarkably similar to each other. The parasitic DNA elements responsible for the exclusions both constitutively synthesize enzymes that are inactive as synthesized by the DNA element but are activated after phage infection by a short peptide determinant encoded by the infecting phage. In the activated state, the enzymes cleave evolutionarily conserved components of the translation apparatus, in one case EF-Tu, and in the other case tRNALys.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

A non-essential domain of Escherichia coli RNA polymerase required for the action of the termination factor Alc.

An evolutionarily nonconserved region of approximately 250 amino acids can be deleted from the amino-terminal part of the beta subunit of Escherichia coli RNA polymerase without effect on the enzyme's basic function. The non-essential segment is located between two highly conserved motifs and is flanked by sequences participating in the rifampicin-binding site. The results define the second non-essential domain in the beta subunit, in addition to the more distal dispensable segment identified previously. The Alc protein of bacteriophage T4 participates in the host transcription shutoff after infection by causing premature termination of transcription on E. coli DNA. Point mutations which prevent Alc action in vivo change amino acids in the non-essential NH2-terminal domain of the beta subunit. These point mutations as well as deletions which remove the non-essential region also prevent Alc action. Thus, in the RNA polymerase molecule, the proximal non-essential domain of beta may function as an acceptor of Alc or other regulatory factors.

Amino Acid Sequence↗
PubMed1994

Translation elongation factor Tu cleaved by a phage-exclusion system.

Bacteriophage T4 multiples poorly in Escherichia coli strains carrying the defective prophage, e14; the e14 prophage contains the lit gene for late inhibitor of T4 in E. coli. The exclusion is caused by the interaction of the e14-encoded protein, Lit, with a short RNA or polypeptide sequence encoded by gol from within the major head protein gene of T4. The interaction between Lit and the gol product causes a severe inhibition of all translation and prevents the transcription of genes downstream of the gol site in the same transcription unit. However, it does not inhibit most transcription, nor does it inhibit replication or affect intracellular levels of ATP. Here we show that the interaction of gol with Lit causes the cleavage of translation elongation factor Tu (EF-Tu) in a region highly conserved from bacteria to humans. The depletion of EF-Tu is at least partly responsible for the inhibition of translation and the phage exclusion. The only other phage-exclusion system to be understood in any detail also attacks a highly conserved cellular component, suggesting that phage-exclusion systems may yield important reagents for studying cellular processes.

Amino Acid Sequence↗