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Biomedical subjects

I Schwartz

Publications and source records attributed to I Schwartz.

At least 91 records · Page 5Linked to original sources
PubMed1991

Growth rate regulation of translation initiation factor IF3 biosynthesis in Escherichia coli.

infC, the gene encoding translation initiation factor IF3 in Escherichia coli, can be transcribed from three promoters. Two of these promoters, PI1 and PI2, are located in the upstream thrS sequence which codes for threonyl-tRNA synthetase. Previous studies had shown that PI2 was the major promoter for infC. In the present study, the extent of transcription from PI1 and/or PI2 at a variety of steady-state growth rates was analyzed by promoter fusion studies. PI2 was the more active promoter (two- to threefold stronger than PI1) at all growth rates tested. A fusion plasmid containing both PI1 and PI2 exhibited a transcription level approximately equal to the sum of those observed with the fusion plasmids containing the individual promoters. The transcriptional activities of PI1 and PI2 did not change as the growth rate was varied from 0.3 to 1.7 doublings per h. In contrast, a fusion plasmid carrying the rrnB P1 promoter displayed the expected growth rate response. The steady-state concentrations of infC mRNA in cells grown at different rates were measured and found not to vary. These results indicate that the previously reported growth rate regulation of IF3 biosynthesis neither is accomplished by transcriptional control nor is a result of differential mRNA stability. In view of these results, the steady-state levels of IF3 in cells grown at a number of different growth rates were determined by quantitative immunoblotting. IF3 levels were found to vary with growth rate in a manner essentially identical to that observed for ribosomes. A model accounting for these results and describing a mechanism for coordinate growth rate-regulated expression of ribosomes and IF3 is presented.

Bacterial Proteins↗
PubMed1991

Nonpalpable ductal carcinoma in situ versus infiltrating carcinoma of the breast--can they be differentiated by mammography?

The radiologic patterns of 193 consecutive women with nonpalpable breast carcinoma were evaluated. The results were correlated with patient age and with the histopathologic diagnosis. Of the 193 women in the study, 135 (70%) were older than 50 years; 102 women had ductal carcinoma in situ, and 67 (62%) of them were over age 50; the remaining 91 women had infiltrating carcinoma, and 73 (80%) of these patients were older than 50 years. Of the 58% of women who presented with microcalcifications, 75% had ductal carcinoma in situ and 25% infiltrating carcinoma. Of the 36% of patients who presented with a mass, 87% had infiltrating carcinoma and 90% were over age 50. Six percent presented with a mass with microcalcifications; 75% of these masses were found to be infiltrating carcinoma. Most of the masses were infiltrating carcinoma, and of these 90% were high-density masses. The small number of masses representing ductal carcinoma in situ were proportionately of low density.

Adult↗
PubMed1990

Base changes at position 792 of Escherichia coli 16S rRNA affect assembly of 70S ribosomes.

To investigate the function of base 792 of 16S rRNA in 30S ribosomes of Escherichia coli, the wild-type (adenine) residue was changed to guanine, cytosine, or uracil by oligonucleotide-directed mutagenesis. Each base change conferred a unique phenotype on the cells. Cells containing plasmid pKK3535 with G792 or T792 showed no difference in generation time in LB broth containing ampicillin, whereas cells with C792 exhibited a 20% increase in generation time in this medium. To study the effect on cell growth of a homogeneous population of mutant ribosomes, the mutations were cloned into the 16S rRNA gene on pKK3535 carrying a spectinomycin-resistance marker (thymine at position 1192), and the cells were grown with spectinomycin. Cells containing G792 or C792 showed 16% and 56% increases in generation time, respectively, and a concomitant decrease in 35S assimilation into proteins. Cells with T792 did not grow in spectinomycin-containing medium. Maxicell analyses indicated decreasing ability to form 70S ribosomes from 30S subunits containing guanine, cytosine, or uracil at position 792 in 16S rRNA. It appeared that C792-containing 30S ribosomes had lost the ability to bind initiation factor 3.

Base Sequence↗
PubMed1990

Function of kidney grafts from brain-dead donor pigs. The influence of dopamine and triiodothyronine.

There are conflicting reports about the effects of administration of dopamine to brain-dead donors upon posttransplant organ function. This study compared the survival and serum creatinine levels in pigs that received renal grafts from untreated controls, from controls in which either the donor or donor and recipient received dopamine or from animals rendered brain dead for 16 hr by acute elevation of intracranial pressure, and given standard supportive treatment. In two additional groups, brain-dead donors were given dopamine or dopamine with triiodothyronine. Recipients of grafts from control animals or from brain-dead donors survived the 7-day period of study and showed minimal changes in serum creatinine. Recipients of grafts from brain-dead donors given dopamine however showed reduced survival and progressive increase in serum creatinine. This did not occur in the group given triiodothyronine concurrently with dopamine. It is suggested that if administration of dopamine is essential to treat donor hypotension, concurrent use of triiodothyronine may preserve posttransplant renal function.

Animals↗
PubMed1990

Cholecystostomy as a definitive operation.

Cholecystostomy for decompression and drainage of the biliary tree is indicated when the elderly, poor risk patient with destructive inflammatory process in the gallbladder is unable to tolerate a more extensive operation. Cholecystostomy is often criticized as an inferior operation, because it provides some palliation but leaves the patient with most problems unattended. To re-evaluate the role of cholecystostomy in the management of acute disease of the gallbladder, we reviewed our experience with it. During the years 1974 to 1987, 37 patients underwent a cholecystostomy. Patients ranged in age from 58 to 90 years, with an average age of 69 years. Twenty-eight patients had acute destructive cholecystitis, usually complicated by perforation, peritonitis or ascending cholangitis. Five had severe pancreatitis; three, cholelithiasis, and one patient, carcinoma of the bladder. Twenty-seven of the 37 patients had severe systemic disease and were critically ill. At the operation, calculi were extracted and the gallbladder and abscess were drained. Two patients died, yielding a mortality rate of 5.4 per cent. Tube cholangiography was done in 33 patients. Although residual stones were demonstrated in seven patients, the stones were removed electively at a later date under much more favorable conditions. None of the 35 survivors had symptoms of disease of the gallbladder during the follow-up period, which ranged from one to 12 years. Cholecystostomy is a curative operation indicated in critically ill and elderly patients for whom extensive operation is a prohibitive risk.

Acute Disease↗
PubMed1989

Perforated adenocarcinoma of the colon during pregnancy.

Performated carcinoma of the colon in pregnant women is a rare event. Only six cases have been reported in the literature, all except one in the recto-sigmoid. We present a case of perforated adenocarcinoma of the colon located above the peritoneal reflection and discuss the problem of diagnosis and management.

Adenocarcinoma↗
PubMed1989

Mexico, maquiladoras, and occupational medicine training.

Industrialization and its concomitant social and environmental effects in developing countries are considered in this paper. Mexico offers one example of economic progress achieved through the promotion of industrial growth. Recognising the need for trained experts with global experience in occupational health, the University of Arizona (UA) has begun a programme to train occupational and preventive medicine residents in international aspects of occupational health in the nearby industrialized border regions of Mexico. By using the maquiladora (assembly plant) industries and the resources of the Instituto Mexicano del Seguro Social with the State of Sonora, residents observe existing problems in occupational safety and health in addition to adding to their understanding of the need for worldwide cooperation for research and reform in this field.

Arizona↗
PubMed1989

Shigellosis in adults: epidemiologic, clinical, and laboratory features.

One hundred and sixteen cases of adult patients hospitalized for shigellosis have been reviewed. The most common presentation included diarrhea (most frequently watery), fever, and abdominal pain, while dysentery has been less frequent. S. flexneri infection, as compared to S. sonnei, was more common in elderly patients and in males, and was characterized by a more prolonged clinical course. Abnormalities of serum electrolytes and hepatic enzymes were the most common laboratory complications, most often seen in elderly patients. Most isolates exhibited susceptibility to the common antimicrobial agents used in shigellosis therapy.

Anti-Bacterial Agents↗
PubMed1988

Kinetic analysis of an E.coli phenylalanine-tRNA synthetase mutant.

A mutation in the pheS gene, encoding phenylalanyl-tRNA synthetase, in E. coli NP37 confers temperature-sensitivity on the organism. A five-fold increase in tRNA(phe) levels complements the mutation. Analysis of the kinetic properties of the mutant enzyme indicates that the KM is 20-fold higher than the wild-type and the dissociation constant of the tRNA(phe)-synthetase complex for the mutant is at least 10-fold higher. These results indicate that the mutation in E. coli NP37 directly affects the tRNA(phe) binding site on the cognate synthetase.

Amino Acyl-tRNA Synthetases↗
PubMed1988

Transcriptional patterns for the thrS-infC-rplT operon of Escherichia coli.

The genes coding for threonyl-tRNA synthetase (thrS), translation initiation factor 3 (infC) and ribosomal protein L20 (rplT) are clustered in the Escherichia coli genome. Previous studies had suggested the possibility that the expression of these genes is coupled. The transcriptional events in this operon have now been examined by S1 nuclease mapping and promoter fusion studies. The results indicate that infC-containing mRNAs are initiated from three separate promoters. Two of these are located in the protein-coding region of thrS and one, P12, is the major promoter at all growth rates tested. In addition, there is co-transcription of thrS and infC from the thrS promoter (PT). A single promoter for thrS has been mapped approx. 170 nucleotides upstream from its translation initiation site. Another promoter has been located within the infC-coding region. It is separated from the next downstream gene, rplT, by a transcription end point. However, termination at this region is only 50-70% efficient and transcripts starting at this promoter can read through into rplT. These findings demonstrate that the pattern of transcription in this operon is highly complex and the mRNA levels for each of the genes is determined by a variety of factors, including multiple promoters, co-transcription and readthrough of transcription termination signals.

Amino Acyl-tRNA Synthetases↗
PubMed1988

Effects of upper dorsal sympathectomy on esophageal motility in humans.

To evaluate the role of the sympathetic nervous system in modulating esophageal motility, esophageal manometry was performed on two groups of patients who underwent upper dorsal sympathectomy for relief of palmar hyperhydrosis. In six patients sympathectomy was done by the supraclavicular approach, with removal of T2 and T3 ganglia. Manometry was performed before the operation and three weeks after it. In seven other patients sympathectomy was done by the axillary approach, with removal of T2-T4 ganglia. Manometry in this group was performed 28.4 +/- 22.4 months after the operation. Fifteen individuals with an intact sympathetic system served as controls. Manometric parameters evaluated were esophageal contraction amplitude and duration and lower esophageal sphincter pressure. The difference between the results obtained in the pre- and postoperative periods in the first group was not statistically significant. The differences between the two patient groups and between the patient groups and the control group were not statistically significant either. We conclude that upper dorsal sympathectomy does not affect esophageal motility in man.

Adolescent↗
PubMed1988

Subdiaphragmatic bronchogenic cyst with communication to the stomach: a case report.

A case of an infradiaphragmatic bronchogenic cyst in an adult patient presenting with nausea, vomiting, and epigastric discomfort is reported. An upper gastrointestinal series showed a multiloculated cyst communicating with the stomach via a patent fistulous tract. At laparotomy the cyst was found to be connected to and communicating with the posterolateral portion of the stomach. The cyst was completely below the diaphragm and received its blood supply from a branch of the abdominal aorta. Histologically, the cyst was composed of smooth muscle, respiratory epithelium, cartilage, and submucous glands. A review of the literature reveals that this case of bronchogenic cyst was unique in that it was located entirely beneath the diaphragm, was not associated with a diaphragmatic hernia or other congenital anomaly, and maintained a patent communication with a portion of the gastrointestinal tract, ie, the stomach, reminiscent of its embryological development.

Bronchogenic Cyst↗
PubMed1988

Traumatic perforations of the esophagus.

Over the past 15 years nine patients with traumatic mechanical perforations of the esophagus have been treated. Seven perforations were iatrogenic, two were accidental. One patient treated conservatively did well. Two patients were operated on without delay. Their hospitalization was short and they had no complications. Six patients were referred to surgery after a delay ranging from 5 days to 17 days from the time of perforation. Their hospitalization ranged from 9 to 113 days, averaging 62.7 days. Complications were common and two patients died. In order to assure survival of patients with esophageal perforation, early aggressive treatment is essential in nearly all instances. In an occasional patient with a small and clean perforation at the esophageal inlet, conservative treatment may be justified.

Adolescent↗
PubMed1987

Diagnosis of pseudoxanthoma elasticum by scar biopsy in patients without characteristic skin lesions.

Pseudoxanthoma elasticum is a disorder of connective tissue that is associated with numerous systemic complications, including accelerated atherosclerosis, gastrointestinal bleeding, angioid streaks in the ocular fundus, and blindness. Diagnosis of the disease is important because many of its complications can be prevented and genetic counseling can be offered to family members of affected patients. The purpose of this study was to examine the usefulness of scar biopsy in establishing a diagnosis of pseudoxanthoma elasticum in patients with angioid streaks but without characteristic skin lesions. Ten patients with angioid streaks but without cutaneous findings indicative of pseudoxanthoma elasticum were evaluated by biopsy of scars and flexural skin. The biopsy specimens were compared with those from unaffected controls. In 6 of the 10 patients, scar biopsies showed fragmentation and clumping of elastic tissue in the deep dermis. Three patients also had these histologic features of pseudoxanthoma elasticum in biopsy specimens of flexural skin that appeared to be normal. We conclude that biopsies of scars in randomly chosen sites may be useful when pseudoxanthoma elasticum is suspected despite the absence of typical skin lesions.

Adult↗