Biomedical subjects

R G Martin

Publications and source records attributed to R G Martin.

At least 19 recordsLinked to original sources

PubMed1998

A novel DNA-binding motif in MarA: the first structure for an AraC family transcriptional activator.

A crystal structure for a member of the AraC prokaryotic transcriptional activator family, MarA, in complex with its cognate DNA-binding site is described. MarA consists of two similar subdomains, each containing a helix-turn-helix DNA-binding motif. The two recognition helices of the motifs are inserted into adjacent major groove segments on the same face of the DNA but are separated by only 27 A thereby bending the DNA by approximately 35 degrees. Extensive interactions between the recognition helices and the DNA major groove provide the sequence specificity.

Amino Acid Sequence↗

PubMed1998

Preparation of uniformly isotope-labeled DNA oligonucleotides for NMR spectroscopy.

Two methods for the large scale preparation of uniformly isotope-labeled DNA for NMR studies have been developed. The first method comprises the growth of a suitable plasmid harboring multiple copies of the desired oligonucleotide in a medium based on 15N and 13C nutrients. The second method uses a polymerase chain reaction (PCR)-based approach with 15N- and/or 13C-labeled deoxynucleoside triphosphates. The novelty of our PCR strategy over existing ones is that the primer and template are the identical molecule, resulting in an exponential growth in the length of the double strand that contains tandem repeats of the target DNA sequence. This novel PCR approach, which we have termed ESRA for endonuclease-sensitive repeat amplification, is easy to use, results in high yields, and can be accomplished at low costs. The utility of both methods is demonstrated for the preparation of a double-stranded 21-mer uniformly labeled with 15N and a double-stranded 17-mer DNA uniformly labeled with 15N and 13C.

Base Sequence↗

PubMed1998

Hodgkin's disease: correlation of clinical characteristics with probabilities for negative lymphangiogram vs. negative laparotomy findings in patients with Stage I supradiaphragmatic presentations vs. those in patients with Stage II.

PURPOSE: At a time both when late complications and second malignancies have become a growing concern and when staging laparotomy has been largely abandoned and comparative studies for staging Hodgkin's disease by state of the art computed tomography (CT) vs. lymphangiography have revealed minimal differences in results for these procedures, our purpose for undertaking this study was twofold. Our initial reason was to determine and compare probabilities for negative abdominal findings for patients with Stage I presentations with those for patients with Stage II as determined by lymphangiography and subsequently by laparotomy for those patients who had negative lymphangiograms. Our second reason, being an extension of the first, was to create a resource that can be used in conjunction with other information for arriving at appropriate treatment decisions including giving either more or particularly less than standard institutional therapy and especially with respect to the abdomen. METHODS AND MATERIALS: Data on 714 patients with prelymphangiogram Stage I-II upper torso presentations of Hodgkin's disease were entered prospectively in our database between 1968 and 1987. Twenty-eight with lymphocyte predominant disease, who had both negative lymphangiogram and negative laparotomy findings and 17 with questionable diagnoses of lymphocyte-depleted or unclassified disease were excluded from subsequent analyses of 669 patients with nodular sclerosis (NS) and mixed cellularity (MC) diagnoses. RESULTS: Stage I: in final logistic models, negative lymphangiogram findings were associated strongly with a combination of no constitutional symptoms and nodular sclerosis histology, whereas negative laparotomy findings correlated strongly with a combination of no constitutional symptoms and female sex. Predicted probabilities depended on the ratios of favorable to unfavorable characteristics. Stage II: in final logistic models, negative lymphangiogram findings were associated strongly with a combination of no constitutional symptoms, nodular sclerosis histology, age <40 years, and <4 involved sites, whereas negative laparotomy findings correlated strongly with a combination of <4 involved sites and mediastinal disease. Predicted probabilities again depended on the ratios of favorable to unfavorable characteristics. CONCLUSION: This study demonstrated that probabilities for negative abdominal findings for patients with supradiaphragmatic presentations of NS and MC Hodgkin's disease depended on: 1) whether the disease presented as Stage I or as Stage II; 2) whether staging was limited to a lymphangiogram or whether it included a laparotomy; and 3) or whether the clinical features associated with the presenting stage and methods of staging were favorable or unfavorable.

Abdomen↗

PubMed1998

Safety and efficacy of intracameral injections of unpreserved lidocaine to reduce intraocular sensation.

PURPOSE: To determine the safety and efficacy of intracameral injections of unpreserved lidocaine to reduce intraocular sensation. SETTING: Carolina Eye Associates, Southern Pines, North Carolina, USA. METHODS: In this prospective study, 100 patients having phacoemulsification under topical anesthesia were randomly assigned to receive an intracameral injection of unpreserved lidocaine (0.5 cc of a 1% unpreserved solution) or balanced salt solution. RESULTS: Ninety-three patients completed the study. There were no significant between-group differences in cell density parameters or Kowa laser flare-cell meter measurements. Seventy-eight percent of lidocaine patients and 56% of controls reported no sensation (P = .048, Fisher's exact test). CONCLUSION: Intracameral injections of unpreserved lidocaine safely and effectively reduced intraocular sensation during phacoemulsification.

Anesthesia, Local↗

PubMed1998

Staar Collamer intraocular lens: clinical results from the phase I FDA core study.

PURPOSE: To assess the early postoperative efficacy and safety of the Staar Collamer intraocular lens (IOL) in small incision cataract surgery. SETTING: Six private ophthalmology practices geographically distributed throughout the United States. METHODS: One hundred twenty-five patients with a mean age of 72.1 years were enrolled in the U.S. Food and Drug Administration (FDA) Phase 1 clinical study of the Staar Collamer IOL after having cataract removal by phacoemulsification. Of these, 107 completed 4 to 6 months of follow-up. RESULTS: At 4 to 6 months postoperatively, 97.1% of patients achieved 20/40 or better corrected visual acuity; 100% of patients without pre-existing pathology (best case) achieved the same result; both results were better than FDA grid values. No persistent sight-threatening complications were reported. Through 6 months, 4.7% of patients required a neodymium:YAG capsulotomy. No IOL dislocations or removals were reported. CONCLUSION: Results indicate that the Collamer material is safe and effective for platehaptic IOLs used in small incision cataract surgery.

Aged↗

PubMed1998

Implantable contact lens for moderate to high myopia: phase 1 FDA clinical study with 6 month follow-up.

PURPOSE: To assess the short-term safety and efficacy of the implantable contact lens (ICL) to treat moderate to high myopia. SETTING: Phase 1 U.S. Food and Drug Administration clinical study of the ICL conducted at four sites in the United States. METHODS: Ten patients with myopia of 7.00 diopters (D) or greater had implantation of a Staar Surgical ICL and were examined preoperatively (baseline) and 1 day, 1 week, and 1, 3, and 6 months postoperatively. Mean preoperative myopia was 7.75 D (range 7.25 to 9.37 D). RESULTS: Six months postoperatively, 5 of 10 eyes (50%) had an uncorrected visual acuity (UCVA) of 20/20 or better, and all eyes had a UCVA of 20/30 or better. All eyes had a best spectacle-corrected visual acuity (BSCVA) of 20/20 or better and 6 eyes (60%), of 20/15 or better. Six eyes (60%) had an improvement of one or more lines of BSCVA. Mean postoperative spherical equivalent was -0.025 D +/- 0.47 (SD). Eight eyes (80%) were within +/- 0.250 D of emmetropia, and all were within +/- 1.125 D. No intraoperative or postoperative complications or adverse reactions were observed. CONCLUSIONS: The results support the short-term safety, efficacy, and predictability of ICL implantation to treat moderate to high myopia.

Adult↗

PubMed1997

Fis, an accessorial factor for transcriptional activation of the mar (multiple antibiotic resistance) promoter of Escherichia coli in the presence of the activator MarA, SoxS, or Rob.

Transcription of the multiple antibiotic resistance marRAB operon increases when one of the sequence-related activators, MarA, SoxS, or Rob, binds to the "marbox" centered at -61.5 relative to the transcriptional start site. Previous deletion analyses showed that an adjacent upstream "accessory region" was needed to augment the marbox-dependent activation. To analyze the roles of the marbox and accessory regions on mar transcription, thirteen promoters, each with a different 5-bp transversion of the -96 to -32 sequence, were synthesized, fused to lacZ, and assayed for beta-galactosidase production in single-copy lysogens with appropriate genotypes. The accessory region is shown here to be a binding site for Fis centered at -81 and to bind Fis, a small DNA-binding and -bending protein, with a Kd of approximately 5 nM. The binding of MarA to the marbox and that of Fis to its site were independent of each other. MarA, SoxS, and Rob each activated the mar promoter 1.5-to 2-fold when it had a wild-type marbox but Fis was absent. In the presence of MarA, SoxS, or Rob, Fis further enhanced the activity of the promoter twofold provided the promoter was also capable of binding Fis. However, in the absence of MarA, SoxS, or Rob or in the absence of a wild-type marbox, Fis nonspecifically lowered the activity of the mar promoter about 25% whether or not a wild-type Fis site was present. Thus, Fis acts as an accessory transcriptional activator at the mar promoter.

Bacterial Proteins↗

PubMed1996

Utilization of endogenous and dietary urea in the large intestine of the mature horse.

The dynamics of N metabolism in mature horses were investigated when they were fed on a low-N diet or the same diet supplemented with sufficient urea or soybean meal to meet their theoretical N requirements. There were no differences in DM, organic matter or neutral-detergent-fibre digestibilities for the three diets. N digestibilities and digestible-N intakes were similar for the urea- and soyabean-supplemented diets and very low for the low-N diet. For all three diets plasma urea was degraded in the digestive tract to NH3 which was utilized by the bacterial population as a N source. NH3 was absorbed from the large intestine into the blood and converted to urea. NH3 was also incorporated into plasma proteins. The horses fed on the low-N diet degraded a greater proportion of endogenous urea in the digestive tract than did horses fed on the urea-or soyabean-supplemented diets. However, the horses fed on the urea diet had the highest degradation rate of urea. The quantity of urea degraded in the digestive tract of horses fed on the urea-supplemented and the low-N diets could not compensate for a lack of dietary crude protein in these diets. The horses were in a negative N balance when fed on the low-N and urea-supplemented diets and a positive N balance when fed on the soyabean-supplemented diet. Dietary urea supplementation did not benefit the horses.

Ammonia↗

PubMed1996

Autoactivation of the marRAB multiple antibiotic resistance operon by the MarA transcriptional activator in Escherichia coli.

Transcriptional activation of the promoters of the mar/soxRS regulons by the sequence-related but independently inducible MarA and SoxS proteins renders Escherichia coli resistant to a broad spectrum of antibiotics and superoxide generators. Here, the effects of MarA and SoxS on transcription of the marRAB promoter itself were assayed in vitro by using a minimal transcription system and in vivo by assaying beta-galactosidase synthesized from marR::lacZ fusions. Purified MarA and MalE-SoxS proteins stimulated mar transcription about 6- and 15-fold, respectively, when the RNA polymerase/DNA ratio was 1. Purified MarA bound as a monomer to a 16-bp "marbox" located 69 to 54 nucleotides upstream of a putative RNA initiation site. Deletion of the marbox reduced MarA-mar binding 100-fold, abolished the stimulatory effects of MarA and SoxS on transcription in vitro, and reduced marR::lacZ synthesis about 4-fold in vivo. Deletion of upstream DNA adjoining the marbox reduced MarA binding efficiency 30-fold and transcriptional activation 2- to 3-fold, providing evidence for an accessory marbox. Although MarA and the mar operon repressor, MarR, bound to independent sites, they competed for promoter DNA in band shift experiments. Assays of marR::lacZ transcriptional fusions in marRAB deletion or soxRS deletion strains showed that the superoxide generator paraquat stimulates mar transcription via soxRS and that salicylate stimulates mar transcription both by antagonizing MarR and by a MarR-independent mechanism. Thus, transcription of the marRAB operon is autorepressed by MarR and autoactivated by MarA at a site that also can be activated by SoxS.

Bacterial Proteins↗

PubMed1995

Binding of purified multiple antibiotic-resistance repressor protein (MarR) to mar operator sequences.

Elevated expression of the marORAB multiple antibiotic-resistance operon enhances the resistance of Escherichia coli to various medically significant antibiotics. Transcription of the operon is repressed in vivo by the marR-encoded protein, MarR, and derepressed by salicylate and certain antibiotics. The possibility that repression results from MarR interacting with the marO operator-promoter region was studied in vitro using purified MarR and a DNA fragment containing marO. MarR formed at least two complexes with marO DNA, bound > 30-fold more tightly to it than to salmon sperm DNA, and protected two separate 21-bp sites within marO from digestion by DNase I. Site I abuts the downstream side of the putative -35 transcription-start signal and includes 4 bp of the -10 signal. Site II begins 13 bp downstream of site I, ending immediately before the first base pair of marR. Site II, approximately 80% homologous to site I, is not required for repression since a site II-deleted mutant (marO133) was repressed in trans by wild-type MarR. The absence of site II did not prevent MarR from complexing with the site I of marO133. Salicylate bound to MarR (Kd approximately 0.5 mM) and weakened the interaction of MarR with sites I and II. Thus, repression of the mar operon, which curbs the antibiotic resistance of E. coli, correlates with the formation of MarR-site I complexes. Salicylate appears to induce the mar operon by binding to MarR and inhibiting complex formation, whereas tetracycline and chloramphenicol, which neither bind MarR nor inhibit complex formation, must induce by an indirect mechanism.

Bacterial Proteins↗

PubMed1995

Wedge resection in the cone after failed refractive surgery in a patient with keratoconus.

A 30-year-old man with keratoconus in the right eye had radial keratotomy in the left eye. Two pairs of corneal relaxing incisions (CRIs) were made in the right eye to flatten the central cornea and reduce high astigmatism. The right eye required an enhancement, and two additional arcuate CRIs were made. A corneal ulcer developed in the right eye, with infiltrates in the incision and corneal thinning. Although the second set of CRIs resulted in more regular astigmatism, the corneal thinning and ulcer caused regression at two months postoperatively. A wedge resection was performed to even the irregular astigmatism. The results are presented.

Adult↗

PubMed1995

Regulation of the multiple antibiotic resistance (mar) regulon by marORA sequences in Escherichia coli.

The mar operon and adjacent sequences were subcloned on a low-copy-number plasmid to identify essential regulatory elements. A 1.1-kbp fragment containing 133 bp of the operator-promoter region (marO), the full marRA gene sequences, and only 10 of 72 marB codons provided a dela mar strain with normal repressibility and inducibility and the ability to beget mar constitutive mutants.

Bacterial Proteins↗

PubMed1995

Purification and regulatory properties of MarA protein, a transcriptional activator of Escherichia coli multiple antibiotic and superoxide resistance promoters.

Expression of the marA or soxS genes is induced by exposure of Escherichia coli to salicylate or superoxides, respectively. This, in turn, enhances the expression of a common set of promoters (the mar/soxRS regulons), resulting in both multiple antibiotic and superoxide resistance. Since MarA protein is highly homologous to SoxS, and since a MalE-SoxS fusion protein has recently been shown to activate soxRS regulon transcription, the ability of MarA to activate transcription of these genes was tested. MarA was overexpressed as a histidine-tagged fusion protein, purified, cleaved with thrombin (leaving one N-terminal histidine residue), and renatured. Like MalE-SoxS, MarA (i) activated the transcription of zwf, fpr, fumC, micF, nfo, and sodA; (ii) required a 21-bp "soxbox" sequence to activate zwf transcription; and (iii) was "ambidextrous," i.e., required the C-terminal domain of the alpha subunit of RNA polymerase for activation of zwf but not fumC or micF. Thus, the mar and soxRS systems use activators with very similar specificities and mechanisms of action to respond to different environmental signals.

Bacterial Proteins↗

PubMed1994

Thin-section contrast-enhanced computed tomography accurately predicts the resectability of malignant pancreatic neoplasms.

A prospective diagnostic study was designed to determine the ability of thin-section contrast-enhanced computed tomography (CT) to predict the resectability of malignant neoplasms of the pancreatic head. Patients with a presumed resectable pancreatic neoplasm referred during a 21-month period were studied with abdominal CT performed at 1.5-mm section thickness and 5-mm slice interval during the bolus phase of intravenous contrast enhancement. CT criteria for resectability included the absence of extrapancreatic disease, no evidence of arterial encasement, and a patent superior mesenteric-portal venous confluence. Of 145 patients evaluated, 42 were considered to have resectable tumors by CT criteria, and 37 (88%) underwent potentially curative pancreaticoduodenectomy. Six patients were found to have a microscopically positive retroperitoneal resection margin; no patient had a grossly positive resection margin. Five (12%) of 42 patients were found at laparotomy to have unresectable, locally advanced or metastatic tumors. Thin-section contrast-enhanced CT is an essential component of the preoperative evaluation for pancreaticoduodenectomy and can prevent needles laparotomy in most patients with locally advanced or metastatic disease.

Adenocarcinoma↗

PubMed1994

Efficacy of diclofenac sodium ophthalmic solution versus placebo in reducing inflammation following cataract extraction and posterior chamber lens implantation.

One hundred forty-eight patients were enrolled in a randomized, prospective, placebo-controlled clinical trial evaluating the efficacy of diclofenac sodium (Voltaren Ophthalmic) in reducing ocular inflammation following extracapsular cataract extraction with posterior chamber intraocular lens implantation. Eligible patients were enrolled and randomized (2:1 diclofenac:placebo) if the sum of anterior chamber cells plus flare one day postoperatively (baseline) was at least four. None of the patients received concomitant steroidal anti-inflammatory treatment. The 99 patients receiving diclofenac sodium had significantly greater improvement from baseline in summed flare plus cell score than the 49 placebo patients at two to five days and seven to nine days after baseline. Similarly, diclofenac sodium patients had significantly less post-baseline conjunctival erythema and ciliary flush than placebo patients. Significantly more diclofenac sodium patients than placebo patients showed moderate to marked improvement from baseline in overall assessment of inflammatory response. Forty-nine percent of placebo patients but only 17% of diclofenac patients were considered therapeutic failures (P < .001). By five to seven days, 82% of diclofenac sodium patients and 59% of placebo patients had corrected visual acuities of 20/40 or better (P < .001). There were no clinically important differences in mean intraocular pressure at any visit.

Aged↗

PubMed1994

The effects of respirator use on workers' productivity in a mentally stressing task.

This article quantitatively determines the effect of wearing half-facepiece respirators, the most widely used type in industry, on worker productivity and efficiency in a mentally stressing task. An experiment investigated the performance of 10 subjects in a task simulating inspection of printed circuit boards. Accuracy and mean reaction time were tested automatically. Paced and unpaced task simulations were used to evaluate the effect of wearing the respirator on response times and the accuracy of subjects' responses for different product complexities and quality levels. The results indicated that wearing the respirator, in general, did not affect the speed or accuracy of subjects performing simulated inspection tasks. Pacing the task resulted in longer response times but did not affect accuracy. More complex products resulted in longer response times but also did not affect accuracy. High product quality resulted in longer response times and a higher miss rate. In terms of accuracy and reaction times a statistically significant difference was found in the performance of subjects.

Adult↗

PubMed1993

When keratometric measurements do not accurately reflect corneal topography.

The keratometer has been the standard for measuring corneal curvature for decades and until recently seemed sufficient for most clinical situations. However, it measures only four points from a small region of the cornea and assumes that the cornea is symmetrical. We document with a number of examples a variety of clinical cases in which keratometry provides either incomplete or frankly misleading information. We believe that corneal topography is now an invaluable clinical tool and will replace the keratometer in standard clinical practice.

Astigmatism↗

PubMed1993

Effect of cataract wound incision size on acute changes in corneal topography.

A randomized prospective trial compared keratometric and visual outcomes for 196 patients receiving 3.2 mm, 5.0 mm, or 6.0 mm incisions for cataract removal and intraocular lens implantation. There were no statistically significant differences among the groups preoperatively or at one to two days or three to six months postoperatively in mean keratometric cylinder, no differences postoperatively in surgically induced cylinder, and no differences in best-corrected visual acuity. Significantly more (P < .01) 3.2 mm cases (75%) had uncorrected visual acuity of 20/40 or better at one to two days postoperatively than 5.0 mm (50%) or 6.0 mm cases (47%). Computer-assisted corneal topographic images were available for the last 56 patients enrolled. Patients receiving 3.2 mm incisions had significantly less wound-related flattening than other patients (P < .05) and tended to have fewer surgically induced changes in corneal shape overall. Changes identified by corneal topography were inconsistent with keratometrically assessed cylinder in 14 patients.

Acute Disease↗