PubMed Health⌕ Search

Biomedical subjects

F Gasser

Publications and source records attributed to F Gasser.

At least 55 records · Page 3Linked to original sources
PubMed1988

Localization of a pyrroloquinoline quinone biosynthesis gene near the methanol dehydrogenase structural gene in Methylobacterium organophilum DSM 760.

A partial Sau3AI genomic bank of Methylobacterium organophilum DSM 760 was constructed in the cosmid pSUP106 and moxF, the structural gene for methanol dehydrogenase, was isolated. In M. organophilum, pSUP106 behaves as a suicide plasmid. This property was used to insert Tn5 into the bacterial chromosome, in the vicinity of moxF, by marker exchange. Mobilization of the Tn5-labelled chromosomal region by a broad-host-range plasmid, pJB3J1 (an R68-45 derivative), allowed the selection of several large R' hybrid plasmids in Escherichia coli HB101. Most of them were able to complement both mutants of the moxF region and mutant MTM1, the first mutant of the pyrroloquinoline quinone (PQQ) biosynthesis pathway in M. organophilum. The gene involved, pqqA, was subcloned and localized.

Alcohol Oxidoreductases↗
PubMed1986

Expression of Tn5-encoded streptomycin resistance in E. coli.

Four Tn5 mutations able to express streptomycin resistance in E. coli were obtained independently. These mutations (called Tn5) were localized and sequenced. All of them consist of a 6 bp deletion in the str gene near the 3' end. The mutation affects a region peculiar for its repetition of an identical 6 bp sequence. The mutation does not affect the level of transcription of the kan, ble, str operon of Tn5, neither does it increase the level of translation of str. The mutation seems to interfere with a post-translational event.

Base Sequence↗
PubMed1986

[Ultra-sensitive TSH levels: an aid in the screening for amiodarone-induced thyroid dysfunction].

Amiodarone modifies thyroid hormone secretion and hypothyroidism occurs in some cases. The latter diagnosis is often difficult and is of particular importance in these patients as it may have serious consequences for the heart. Early diagnosis is therefore essential but difficult because of the induced hyperthyroxinemia with maintenance of euthyroidism and a hypotriiodothyronemia. The diagnostic performance of an ultrasensitive method of measuring TSH (TSH-U), capable of distinguishing hyper and euthyroidism were compared with standard thyroid function tests and TSH stimulation with TRH in 50 patients treated with amiodarone. Only 6 of the 14 patients with hyperthyroxinaemia had TSH-U values in the hyperthyroid range: only one of these patients had an increased triiodothyronine. In 2 cases the THS-U was low but the T4L was normal. In 4 patients, increased TSH-U allowed diagnosis of latent or patent hypothyroidism. There was a close correlation between results of the TRH stimulation test and those of the TSH-U in all cases. This test may therefore be used as an initial screening test for thyroid dysfunction in patients on amiodarone and is simple, reliable and relatively cheap to perform. It makes it unnecessary to measure all thyroid hormonal parameters and the TRH test simultaneously.

Amiodarone↗
PubMed1986

[The ultrasensitive determination of TSH permits the prediction of the response to TSH in the TRH test].

A new ultrasensitive TSH immunoradiometric assay (IRMA) using two monoclonal antibodies is now able to distinguish between euthyroid and hyperthyroid patients. The aim of this study was to compare data given by ultrasensitive basal TSH (IRMA) and by the response of TSH to TRH test considered until now as the more reliable test in case of mild or atypical hyperthyroidism. Basal plasma TSH levels were determined in euthyroid (n = 80), hyperthyroid (n = 30), hypothyroid (n = 14) and pituitary deficient patients (n = 8) before and 30 minutes after a TRH test (250 micrograms i.v.). A close linear correlation was found between basal and post-stimulative TSH levels. Normal TSH response ranged from 2 to 22 uU/ml. The sensibility and the specificity of these two parameters appeared comparable in the case of primary dysthyroidism; on the contrary basal TSH levels were not sufficient for the diagnosis of central hypothyroidism. In conclusion, excepted for pituitary deficiency, basal plasma TSH (IRMA) levels are accurate and sufficient in the evaluation of the thyroid function and make the TRH-test useless.

Humans↗
PubMed1985

Completion of the nucleotide sequence of the central region of Tn5 confirms the presence of three resistance genes.

The DNA sequence of the region located downstream from the kanamycin resistance gene of Tn5 up to the right inverted repeat IS50R has been determined. This completes the determination of the sequence of Tn5 which is 5818 bp long. The 2.7 Kb central region contains three resistance genes: the kanamycin-neomycin resistance gene, a gene coding for resistance to CL990 an antimitotic-antibiotic compound of the bleomycin family and a third gene that confers streptomycin resistance in some bacterial species but is cryptic in E. coli. A Tn5* mutant able to express streptomycin resistance in E. coli was isolated. With this mutant, it was demonstrated that in E. coli the expression of the three resistance genes is coordinated in a single operon.

Amino Acid Sequence↗
PubMed1985

Long-term multiplication of the Chinese hamster ovary (CHO) cell line in a serum-free medium.

A new synthetic medium (referred to as GC3) that supports the growth of the Chinese hamster ovary cell line has been developed. It is composed of a 1:1 mixture of Ham's F12 and modified Eagle's minimum essential (MEM.S) mediums supplemented with transferrin (10 micrograms/ml), insulin (80 mU/ml), and selenium (1 X 10(-7) M). Other more simple supplementations of our basal medium MEM.S/F12 (transferrin + insulin, transferrin + selenium, ferrous iron + selenium) also give good cell growth responses. Fibronectin or serum pretreatment is not needed for cellular attachment and spreading. Our culture system is characterized by a continuous serum-free cultivation (more than 200 doublings), a clonal growth, a high density proliferation, and a rapid growth rate near that of cells in serum-supplemented medium.

Animals↗
PubMed1984

Comparison of two bacterial azoreductases acquired during adaptation to growth on azo dyes.

Selection for utilization of carboxy-Orange I [1-(4'-carboxyphenylazo)-4-naphthol] in the chemostat yielded Pseudomonas strain K24 which was unable to grow on carboxy-Orange II [1-(4'-carboxyphenylazo)-2-naphthol] while selection for growth on carboxy-Orange II had previously led to strain KF46 which did not utilize carboxy-Orange I. Orange I azoreductase of strain K24, the key enzyme of dye degradation, was purified 80-fold with 17% yield to electrophoretic homogeneity and compared to the previously purified Orange II azoreductase of strain KF46. Common properties of the two enzymes were their monomeric structure, their specificity for NADPH and NADH as cosubstrates, the range of their Km values for substrates and cosubstrates as well as their reactivity towards a series of substrate analogs. They differed from each other with respect to molecular weight (21,000 and 30,000) and in the absolute requirement of Orange I azoreductase for a hydroxy group in the 4'position of the naphthol ring of the substrate molecule as compared to the requirement for substrates with a 2-naphthol moiety by Orange II azoreductase. The pure enzymes did not exhibit immunological cross-reaction with each other. Crude extracts of strains K24 and KF46 and of azoreductase-negative strains isolated at different stages of the adaptation experiments, however, contained material which cross-reacted (CRM) with both anti Orange I azoreductase serum and anti Orange II azoreductase serum. The CRM may represent a common precursor protein of the azoreductases in strains K24 and KF46.

Adaptation, Physiological↗