Search PubMed⌕ Search

Biomedical subjects

D L Johnson

Publications and source records attributed to D L Johnson.

At least 235 records · Page 13Linked to original sources
PubMed1989

Identification of a 150-kilodalton polypeptide that copurifies with yeast TFIIIC and binds specifically to tRNA genes.

The transcription in vitro of eucaryotic tRNA genes by RNA polymerase III requires two transcription factors, designated TFIIIB and TFIIIC. One of the critical functions of TFIIIC in the transcription of tRNA genes is that it interacts directly and specifically with the two internal promoter elements of these genes. We have partially purified Saccharomyces cerevisiae TFIIIC by chromatography on Bio-Rex 70, DEAE-cellulose, and phosphocellulose resins. A 150-kilodalton (kDa) DNA-binding polypeptide copurified with TFIIIC activity. This 150-kDa protein coeluted with the DNA-binding activity of TFIIIC after rechromatography of TFIIIC on phosphocellulose and its elution with a linear salt gradient. The stable and high-affinity interaction of this protein with tRNA genes was demonstrated by the maintenance of a protein-DNA complex under conditions of high ionic strength. Finally, we showed by two criteria that the interaction of this protein with tRNA genes was specific. First, the protein-DNA complex was competed with only by DNA-containing tRNA genes; second, the protein preferentially bound to DNA fragments containing a tRNA gene. These results strongly suggest that the DNA-binding domain of the yeast TFIIIC is contained within this 150-kDa polypeptide.

Binding Sites↗
PubMed1989

Management of choroid plexus tumors in children.

Choroid plexus tumors are most common in the first year of life and are quite large at presentation. Total resection is the treatment of choice, and many children require diversion of the cerebrospinal fluid despite removal of the tumor. Tumor size and associated hydrocephalus present formidable challenges to the pediatric neurosurgeon. The operative approaches as well as other treatment options are discussed.

Adolescent↗
PubMed1989

Nephrotic syndrome: a nursing care plan based on current pathophysiologic concepts.

The classic conception of the pathophysiology of the nephrotic syndrome (NS) is now being seriously questioned, on the basis of current research findings. New conceptions of the syndrome, with its proteinuria, hypoalbuminemia, and edema, are providing explanations for the discrepancies between the original theory and clinical data from individual patients, particularly related to edema formation. Many of the edema-preventing mechanisms are normal in patients with NS, but may fail when plasma osmotic pressure falls significantly. Plasma volumes, blood volumes, and blood pressures of patients with NS have been found to be generally normal or slightly increased, in contrast to the classic "hypovolemia" theory. Activation of the renin-angiotension-aldosterone system is variable and cannot fully explain the sodium and water retention. The decreased renal filtration rates and abnormal sodium retention/excretion rates are now best explained by an intrarenal defect, on the basis of multiple research approaches. These research conceptions of the pathophysiology of NS are significant for nurses because they can be used in patient assessment, interpretation of patient data, monitoring during treatment, collaboration about the plan of care, development of nursing care plans, and patient teaching. Several nursing diagnoses may be appropriate for patients with NS: alteration in fluid volume: excess; potential for infection; alteration in nutrition: less than body requirements, potential alteration in comfort; knowledge deficit; and potential disturbance in self-concept: body image.

Humans↗
PubMed1988

Reducing intraoperative myocardial acidosis by continuous cardioplegic perfusion via the coronary sinus.

Continuous retrograde coronary sinus perfusion (RCSP) can deliver cardioplegic solution homogeneously to the myocardium via the disease-free venous system. However, administration of cardioplegic solution through the coronary venous system necessitates low pressure infusion which may limit the rate of cardioplegic delivery. In addition, infusion of the solution at low flow rates may not prevent the development of myocardial acidosis during arrest. To determine if RCSP is capable of limiting intraoperative myocardial acidosis, open-chest pigs, monitored by intramyocardial pH probes, underwent cardioplegic arrest with a single dose aortic root infusion followed by a 45-min period of no RCSP (Group 1), RCSP of 25 mEq/liter bicarbonate-buffered cardioplegic solution (Group 2), RCSP of blood-buffered cardioplegic solution (Group 3), and RCSP of histidine-buffered cardioplegic solution (Group 4). There were no significant differences between the groups with respect to baseline pH, with a range of 7.27 to 7.32. At the end of the 45-min arrest period, Group 2 had a statistically higher pH, 7.06 +/- 0.08, compared to Group 1, 6.74 +/- 0.08 (P less than 0.05). Hearts in Groups 3 and 4 demonstrated preservation of preischemic pH levels after 45 min of arrest, 7.29 +/- 0.07 and 7.37 +/- 0.10, respectively, significantly higher than either Group 1 or 2 (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1988

The long-term success of skeletal muscle in aortic repair.

To determine the efficacy of skeletal muscle for aortic repair, 23 swine underwent repair of descending thoracic aortic defects. In one group, a vascularized muscle flap was used to patch a 2- to 3-cm aortic defect. In two other groups, a short segment of aorta was removed and a 2-cm tube graft of freshly harvested but devascularized skeletal muscle or Vicryl mesh was used to repair the aorta. Swine were followed for up to sixteen months after implantation. There were no deaths or graft-related complications in the vascularized muscle patch group, and after sixteen months, there were no stenoses or aneurysmal dilatations of the flaps. Histologically, a mature pseudointimal layer had been deposited under the muscle flap and was grossly indistinguishable from normal arterial wall. In the group that received devascularized muscle tube grafts, however, suture line dehiscences occurred in 3 of 7 animals within two weeks of operation. There were no dehiscences in the 9 recipients of a Vicryl tube graft, a finding suggesting that deposition of pseudointimal elements was rapid enough to ensure vascular integrity as the Vicryl was absorbed. Postmortem examination of these animals demonstrated stenoses ranging from 30 to 50%, thereby indicating a lack of growth in the new pseudointimal wall. These results demonstrate the long-term reliability of vascularized skeletal muscle for use in major vascular reconstruction, and suggest the beneficial effects of avoiding prosthetic material and promoting optimal pseudointimal formation.

Animals↗
PubMed1988

Treatment of intracranial abscesses associated with sinusitis in children and adolescents.

We retrospectively reviewed the management of intracranial abscesses associated with sinusitis in 13 children and adolescents by reviewing medical records and computed tomography (CT) scans of a consecutive case series. The mean duration of follow-up was 4.5 years with a range of 1.3 to 8.6 years, and the setting was a major metropolitan children's hospital providing primary as well as tertiary care. All patients received antibiotics (most commonly chloramphenicol, 75 to 100 mg/kg/day, in combination with oxacillin, 150 to 200 mg/kg/day) to which the sinus and intracranial organisms are susceptible. Surgical drainage of loculated infection was done for patients with acute neurologic symptoms or signs and for those patients whose abscesses enlarged during medical therapy. Three patients underwent immediate drainage of intracranial abscesses because of acute neurologic signs and symptoms. Sequential CT scans demonstrated enlargement of the intracranial abscesses in the remaining 10 patients. This apparent failure of medical management could not be explained by duration of symptoms before therapy, size of lesion, choice of antibiotics, or use of steroids. No child was successfully treated with antibiotics alone. Successful management consisted of antibiotic therapy combined with surgical drainage of loculated infection. This approach to therapy is preferred for all children with intracranial abscess associated with sinusitis.

Adolescent↗
PubMed1988

cDNA cloning of human liver monoamine oxidase A and B: molecular basis of differences in enzymatic properties.

The monoamine oxidases play a vital role in the metabolism of biogenic amines in the central nervous system and in peripheral tissues. Using oligonucleotide probes derived from three sequenced peptide fragments, we have isolated cDNA clones that encode the A and B forms of monoamine oxidase and have determined the nucleotide sequences of these cDNAs. Comparison of the deduced amino acid sequences shows that the A and B forms have subunit molecular weights of 59,700 and 58,800, respectively, and have 70% sequence identity. Both sequences contain the pentapeptide Ser-Gly-Gly-Cys-Tyr, in which the obligatory cofactor FAD is covalently bound to cysteine. Based on differences in primary amino acid sequences and RNA gel blot analysis of mRNAs, the A and B forms of monoamine oxidase appear to be derived from separate genes.

Amino Acid Sequence↗
PubMed1988

Isolation and comparison of Escherichia coli strains from canine and human patients with urinary tract infections.

We analyzed Escherichia coli strains isolated from dogs with urinary tract infections (UTIs) in an attempt to determine if any of these strains were similar to E. coli isolated from humans with UTIs. Using genotypic and phenotypic traits, we identified four canine and six human E. coli UTI isolates that all appeared to be closely related or identical. All isolates shared similar DNA sequences for pyelonephritis-associated pili (pap), alpha-hemolysin (hly), and insertion sequence 5 (IS5), on the basis of Southern blot analysis. Similar outer membrane protein, pilin, and plasmid profiles were obtained for each of the isolates, although minor heterogeneity was observed. All of these isolates expressed a neuraminidase-sensitive binding phenotype in contrast to the majority of human isolates, which are known to express an adhesin that recognizes terminal digalactoside residues. Taken together, these results suggest that similar E. coli uropathogens may be capable of infecting both dogs and humans. To determine if the intestinal tracts of dogs were a reservoir for uropathogenic E. coli, eight paired rectal and urine pap+ E. coli strains were cultured from dogs with UTIs. By using the same genotypic and phenotypic criteria described above as a basis for strain identity, seven of eight urine-rectal pairs showed intrapair identity. However, each urine-rectal pair displayed a unique overall profile and could be distinguished from the other pairs. We conclude that the uropathogen colonizing the bladders of dog can also be the predominant strain colonizing the intestinal tracts.

Animals↗
PubMed1988

Fixed spinal cord: diagnosis with MR imaging.

Pulsatile motion of the spinal cord was examined with phase imaging techniques. Sagittal images of the spinal cord were obtained at different times of the cardiac cycle in healthy volunteers, as well as in patients in whom the spinal cord either was tethered, was compressed, or contained an intramedullary lesion. Pulsatile velocity changes of the spinal cord, observed on the phase images, were most marked at the cervical-upper thoracic level. Cord motion was found to be significantly decreased in cases in which the cord was either tethered or compressed. Cord enlargement due to an intramedullary lesion generally did not lead to decreased cord motion. Imaging of pulsatile cord motion may be clinically useful in evaluating diseases restricting cord motion or changing the status of parenchymal compliance.

Adult↗
PubMed1988

New pluronic-free perfluorocarbon cardioplegia improves myocardial oxygenation.

Cardioplegic protection with oxygenated lecithin-emulsified methyl adamantane, a perfluorocarbon with high oxygen solubility, was compared with oxygenated crystalloid cardioplegic solution in an ischemic rabbit heart model. The cardioplegic solutions had identical salt compositions with a potassium concentration of 15 meq/l. Eighteen isolated rabbit hearts underwent 180 minutes of global ischemia at 30 degrees C, followed by a 45-minute period of reperfusion at 37 degrees C. During the ischemic period, cardioplegic solution was infused every 30 minutes, and myocardial oxygen extraction was calculated. Left ventricular function was assessed before and after ischemia by measuring left ventricular isovolumic developed pressure and the first derivative of pressure (dP/dt). Cardioplegia oxygen extraction for the methyl adamantane hearts was 230 +/- 11 ml of O2/100 g heart wt and 150 +/- 25 ml O2/100 g heart wt for the crystalloid hearts (p less than 0.05). Recovery of dP/dt at 30 minutes of reperfusion, expressed as a percentage of preischemic control, was 80% +/- 3% for the methyl adamantane hearts and 61% +/- 3% for the crystalloid hearts (p less than 0.05). The developed pressure for the methyl adamantane hearts was 73% +/- 3% and for the crystalloid hearts, 62% +/- 2% (p less than 0.05). In this global ischemia model, perfluorocarbon emulsified with egg-yolk phospholipid improved oxygen delivery and postischemic myocardial performance compared with an oxygenated crystalloid cardioplegic solution.

Animals↗
PubMed1987

Evidence for in vitro translesion DNA synthesis past a site-specific aminofluorene adduct.

The ability of Escherichia coli DNA polymerase I and T7 DNA polymerase to bypass bulky C-8 guanyl-2-aminofluorene adducts in DNA was studied by in vitro DNA synthesis reactions on a site-specific aminofluorene-modified M13mp9 template. This site-specifically modified DNA was prepared by ligating an oligonucleotide containing a single aminofluorene adduct into a gapped heteroduplex of M13mp9 DNA (Johnson, D. L., Reid, T. M., Lee, M.-S., King, C. M., and Romano, L. J. (1986) Biochemistry 25, 449-456). The resulting covalently closed duplex DNA molecule was then cleaved with a restriction endonuclease, denatured, and annealed to a primer on the 3' side of the adduct to form a template specifically designed to study bypass. In this system, any synthesis that was not blocked by the bulky aminofluorene adduct would proceed to the 5' terminus of the single-stranded template, while synthesis interrupted by the adduct would terminate at or near the adduct location. We have measured DNA synthesis on this template and find that the amount of radiolabeled nucleotide incorporated by either E. coli DNA polymerase I (large fragment) or T7 DNA polymerase was much greater than would be predicted if the aminofluorene adduct were an absolute block to DNA synthesis. Furthermore, the products of similar reactions electrophoresed on polyacrylamide gels showed conclusively that the majority of the DNA synthesized by either the T7 DNA polymerase or E. coli DNA polymerase I bypassed the aminofluorene lesion. Substitution of Mn2+ for Mg2+ as the divalent cation resulted in even higher levels of translesion synthesis.

2-Acetylaminofluorene↗
PubMed1987

Primary prevention of behavior problems in Mexican-American children.

A primary prevention program, the Houston Parent-Child Development Center, directed towards infants and their parents, has effectively reduced the frequency of behavior problems for these children 5 to 8 years after the program's completion. Teacher ratings showed significantly fewer acting-out, aggressive behaviors for program children. Ratings of classroom behaviors found program children significantly less hostile and more considerate than control boys. This appears to be the first primary prevention program to have demonstrated effectiveness in reducing behavior problems over such a long time.

Aggression↗
PubMed1987

Chemical stability of oligonucleotides containing the acetylated and deacetylated adducts of the carcinogen N-2-acetylaminofluorene.

We have prepared and characterized the single-stranded oligonucleotide heptamer 5'-ATCCGTC-3' in which the lone guanine of the oligonucleotide is modified at the C8 position with either the acetylated or deacetylated form of the carcinogenic adduct 2-aminofluorene. These two lesions represent the two major adducts formed upon the in vivo administration of the potent experimental carcinogen N-2-acetylaminofluorene. The stability of the adducts was compared by analyzing the oligonucleotide for strand scission or depurination by polyacrylamide gel electrophoresis following treatment under either neutral, acidic or basic conditions or incubation in the presence of piperidine. The results show that both adducts are stable near neutral pH but that the deacetylated adduct is less stable than the acetylated adduct to either basic or acidic conditions. Both adducts are equally susceptible to piperidine. The method of analysis described here could prove useful for characterizing other adduct structures, thus providing a general procedure to determine the stability of a variety of lesions in DNA.

2-Acetylaminofluorene↗
PubMed1987

Use of connected discourse tracking to train functional speech skills.

The connected discourse tracking procedure was adopted for use as a production training task for profoundly hearing-impaired children. A clinician served as the receiver and 5 children with profound hearing losses each served as the sender for 16 tracking sessions. There were individual differences among the children in their ability to convey the connected discourse to the clinician over time. The increase in comprehension of each subject's speech during the last session relative to the amount of information understood during the first session ranged from 0 to 48%. Two independent observers were used during the first and last sessions to verify the tracking results obtained by the clinician (the primary receiver). There were differences in words tracked per minute among the three receivers with the primary clinician achieving higher tracking rates than the other two. The children learned how to use discourse strategies when they were not understood and they were highly motivated by the task. The results indicate that it is feasible to incorporate the procedure in a speech training program for hearing-impaired children.

Adolescent↗
PubMed1987

Intraventricular hemorrhage in the newborn beagle puppy. A limited model of intraventricular hemorrhage in the premature infant.

The term beagle puppy has been used extensively as an experimental model of intraventricular hemorrhage (IVH) in the preterm infant. Fourteen variables were selected which were considered theoretically important to both the model and the preterm infant, and the data were subjected to discriminant analysis. Use of only three variables in combination correctly predicted whether an animal would sustain germinal matrix hemorrhage: baseline blood pressure, Pco2, and temperature. The model does not involve ischemia, which appears to be the sentinel but not singular insult in the IVH of preterm infants.

Animals↗