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Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 811 records · Page 45Linked to original sources
PubMed1978

N4-Acetylcytidine. A previously unidentified labile component of the small subunit of eukaryotic ribosomes.

The nucleoside content of 18 S rRNA from rat liver is determined under conditions known to prevent the destruction of chemically labile modified nucleosides. Two base-modified nucleosides, not completely identified before, are shown to be N6-methyladenosine and 7-methylguanosine. The results further demonstrate the presence of a hitherto unidentified component of 18 S rRNA whose spectra and chromatographic properties are identical with that of N4-acetylcytidine. In addition, this compound is not detectable in 28 S rRNA nor in 16 S rRNA derived from the small ribosomal subunit of Escherichia coli. However, it appears to be conserved in the small ribosomal subunit of eukaryotes, since it is also present in yeast 17 S rRNA and chicken liver 18 S rRNA.

Animals↗
PubMed1978

Inhibitors of gastric lesions in the rat.

The production by stress of gastric lesions in rats was inhibited by metiamide and by mepyramine. Lesions induced by indomethacin treatment were inhibited by mepyramine but not by metiamide. Those induced by aspirin treatment in pylorus-ligated rats were not affected by either antihistamine drug. Oral glutamine inhibited lesion production in all three systems whereas aspirin orally markedly potentiated it. Sodium salicylate inhibited both indomethacin-induced lesions and those produced by aspirin in pylorus-ligated rats. On the other hand, copper salicylate inhibited stress-induced lesions and it, like copper aspirinate, also markedly reduced the extent of lesions produced by aspirin. On the basis of these results, stress-induced lesion production offers a suitable animal model for testing anti-ulcer drugs as it is, like most human gastric ulcers, inhibited by H2-receptor inhibitors like metiamide.

Animals↗
PubMed1978

Sweat testing for cystic fibrosis. Diagnostic screening with a combination chloride ion-selective electrode.

Screening of sweat chloride in newborn infants with the Orion Skin Chloride Measuring System and incorporating some procedural innovations is described. The results indicate that while diagnostic screening for cystic fibrosis can be readily undertaken, the test with the chloride ion-selective electrode is best left at least to the second day of life or later because of insufficient sweating in very young babies. Measurements on 2 babies with cystic fibrosis are also discussed.

Age Factors↗
PubMed1978

Altered myocardial function and collagen in diabetic rhesus monkeys on atherogenic diet.

We have demonstrated that in rhesus monkeys, 18 months of diabetes alters the end-diastolic pressure, end-diastolic volume relations without hypertrophy. Accumulation of collagen in the myocardial interstitium was the apparent basis for abnormal left ventricular performance. Neither collagen concentration nor left ventricular performance were signigicantly affected by dietary lipid composition. These myocardial abnormalities occurred at a stage when coronary atherosclerosis was limited. However, the relative influence of coronary atherosclerosis and myocardial alterations during more prolonged lipid feeding remains to be determined.

Animals↗
PubMed1977

[4-Thiouridine and photoprotection in Escherichia coli K 12].

A high level of protection is observed in the Escherichia coli K 12 strain AB 1157 rec A 1 nuv+ whose transfer RNA contains 4-thiouridine. In contrast, the photoprotection level is low and observed at higher doses in a strain which differs from the former by a single mutation, nuv-, (lack of 4-thiouridine). This nucleoside is therefore an important chromophore leading to photoprotection. This conclusion is corroborated by the similarity of the action spectra for 8-13 link formation in tRNA and for photoprotection.

Cell Survival↗
PubMed1977

[Genetic localization of a mutation rendering the growth of E coli K12 insensitive to illumination at 365 nm].

The genotype of the Nop mutant recently isolated from the E. coli K 12 strain AB 1157 has been characterized. This mutant lacks 4-thiouridine in its tRNA and is much less susceptible to near ultraviolet-induced growth delay than wild type cells. This phenotype results from a single mutation called nuv which has been localized on the E. coli genetic map. nuv is found by conjugation to lie between the origins of injection of Hfr P4X and Hfr cavalli in the vicinity of the lac gene. Cotrans-duction with bacteriophage P1 more precisely maps nuv at 0.3 min. clockwise from tsx.

Conjugation, Genetic↗
PubMed1977

Role of divalent ions in folding of tRNA.

The native structure of tRNA is not achieved in low salt (4.5 mM Na+, 25 degrees C), but can be restored by addition of divalent ions. We have explored the structure of the central region in Escherichia coli tRNAfMet by absorption and emission spectroscopy of 4-thiouracil, and the structure of the anticodon loop in yeast tRNAPhe by fluorescence of the 'Y' base, versus the number of manganese ions bound to tRNA, which was derived from electron spin resonance. The fluorescence of the reduced 8-13 photoproduct (in which 4-thiouracil at position 8 is crosslinked to cytosine at position 13) was also analysed. In low salt (e.g. 4.5 mM Na+), the region of 4-thiouracil is affected strongly as the first eight Mn2+ bind to tRNA, whereas the fluorescence of the 'Y' base is affected only after four Mn2+ are bound. Considering the structural similarities of the two tRNAs, this suggests that the reorganisation brought about by divalent ions starts in the central region, the anticodon loop being affected later. The binding of divalent ions to each region starts together with its restructuration. Monovalent ions can substitute for divalent ions in this process, a 15 mM sodium concentration being equivalent to the binding of the first five Mn2+. If divalent ions are then added, even the first ones distribute themselves between both the central and the anticodon region. Alternatively, the renaturation may be achieved by monovalent ions only, implying that no sites exist whose occupancy by divalent ions is crucial for the native structure. These observations suggest that the role and means of divalent ion binding to tRNA are largely explainable in terms of a simple maganese-phosphate binding supplemented by electrostatic interaction with distant phosphates.

Anticodon↗
PubMed1977

[Mutants of Escherichia coli deficient in 4-thiouridine in which growth is insensitive to illumination at 365 nm].

Thirteen different mutants of E coli K12 selected for a reduced near ultra-violet induced growth delay have been isolated. The t-RNAs extracted from these clones have all a depressed content of 4-thiouridine. One of these mutants, called Nop has an almost negligible growth delay and completely lacks 4-thiouridine in its t-RNAs. Thus we provide genetic proofs that 4-thiouridine is the chromophore for growth delay.

Escherichia coli↗
PubMed1977

Free-living volunteer's motivations and attitudes toward pharmacologic studies in man.

Two groups of volunteers who had participated in pharmacologic studies were interviewed about their impressions of such studies. One group was from a university community, the other from the pharmaceutical industry. The differences between the two groups were correlated with their respective backgrounds. Both groups had favorable impressions about drug studies and investigators. Most were satisfied with the information given them about the nature and risks of the studies, but some believed that a written description of the study that they could consult at home would improve their understanding of the information. Financial reward was the primary reason given by both groups for volunteering, but the perceived risk of the study was the ultimate deciding factor. The volunteers disliked having their mobility restricted and for this reason might not be willing to participate in long-term studies, such as those formerly carried out in prisons. Alternative sources of volunteers for long-term studies will have to be found.

Adult↗
PubMed1977

Pancreatic perinuclear inclusions in diabetes mellitus and other diseases.

Unusual perinuclear inclusions in pancreatic duct cells were observed by electron microscopy in 23 diabetic pancreases, in nine pancreases with islet hyperplasia, and in 10 of 27 pancreases without islet pathology. The origin and significance of the perinuclear inclusions could not be determined, but it is suggested that they may be of viral origin or may represent a cellular response to an unknown stimulus.

Adolescent↗