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Biomedical subjects

J C Boyer

Publications and source records attributed to J C Boyer.

47 records · Page 3Linked to original sources
PubMed1988

Overlapping open reading frames revealed by complete nucleotide sequencing of turnip yellow mosaic virus genomic RNA.

The complete nucleotide sequence of turnip yellow mosaic virus (TYMV) genomic RNA has been determined on a set of overlapping cDNA clones using a sequential sequencing strategy. The RNA is 6318 nucleotides long, excluding the cap structure. The genome organization deduced from the sequence confirms previous results of in vitro translation. A novel open reading frame (ORF) putatively encoding a Pro-rich and very basic 69K (K = kilodalton) protein is detected at the 5' end of the genome. It is initiated at the first AUG codon on the RNA and overlaps the major ORF that encodes the non structural 206K (previously referred to as 195K) protein of TYMV; its function is unknown. Several amino acid consensus sequences already described among plant and animal viruses are also found in the TYMV-encoded polypeptides. A comparison with other viruses whose RNA sequence is known leads to the conclusion that TYMV belongs to the "Sindbis-like" supergroup of viruses and could be related to Semliki forest virus.

Amino Acid Sequence↗
PubMed1988

Plant viruses and new perspectives in cross-protection.

Cross-protection in plants is the phenomenon whereby a plant preinoculated with a mild virus strain becomes resistant to subsequent inoculation by a related severe strain. It has been used on a large scale in cases where no resistant plants are available. Although several hypotheses have been proposed to explain the molecular mechanism underlying cross-protection, no single hypothesis can account for all the data obtained. Recently, a phenomenon akin to cross-protection has been achieved in transformed plants harboring the cDNA of a part of a viral RNA genome. These results obtained by genetic engineering raise new hopes for obtaining plants resistant to virus infection.

Genetic Engineering↗
PubMed1986

Effect of benzo[a]pyrene-diol-epoxide-I on growth of nascent DNA in synchronized human fibroblasts.

In logarithmically growing cultures of human fibroblasts, benzo[a]pyrene-diol-epoxide-I (BPDE-I) treatment inhibits both replicon initiation and DNA chain elongation. In this study we have focused on the effect of BPDE-I treatment on the growth of nascent DNA strands in synchronized human fibroblasts. Cells were collected at the beginning of the S phase by replating confluent cultures in the presence of aphidicolin for 24 h. At 1 h after release from aphidicolin, cells were incubated with [3H]thymidine for 10-15 min and treated with BPDE-I for 10 min. Following different periods of incubation with unlabeled thymidine, cells were lysed on top of alkaline sucrose gradients for analysis of the size distribution of nascent DNA and its average molecular weight. After a brief pulse with the radiolabeled precursor, a unimodal distribution of nascent DNA strands was observed in control cells. Upon chase this distribution was displaced to higher average molecular weights at an approximate rate of 1 X 10(6) daltons/min. Treatment with low doses of BPDE-I (less than 0.2 microM) did not decrease this rate. Indeed the nascent DNA in BPDE-I-treated cells appeared to grow faster than in control cells. This higher rate of DNA strand growth may be related to the inhibition of replicon initiation. Treatment with 0.3 microM or 0.7 microM BPDE-I, which are doses that interfere with DNA synthesis in operating replicons in asynchronous cells, also inhibited the growth of nascent DNA strands in synchronized cells by 22 and 64%, respectively. Because of the simultaneous inhibition of replicon initiation, these values are probably underestimations of the total inhibition of DNA strand growth. The use of synchronized cells in this type of study should aid in the elucidation of mechanisms of replication of carcinogen-damaged DNA.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1986

Xeroderma pigmentosum variant and normal fibroblasts show the same response to the inhibition of DNA replication by benzo[a]pyrene-diol-epoxide-I.

Xeroderma pigmentosum (XP) variant cells are characterized by an abnormal pattern of replication of DNA damaged by 254 nm radiation (u.v.). To see whether benzo[a]pyrene-diol-epoxide-I (BPDE-I) elicits the same response, we have compared the effects of u.v. and BPDE-I on DNA replication in XP variant and normal skin fibroblasts. Doses of u.v. that only affected replicon initiation in normal cells, inhibited DNA strand growth in the XP variant. These results were confirmed by measurements of the rate of growth of single-stranded nascent DNA in cells synchronized at the beginning of the S phase. Identical analyses using BPDE-I, however, indicated that the two cell types were equally sensitive to the inhibitions of both replicon initiation and DNA strand growth. These results indicate that the XP variant phenotype cannot be recognized in vitro by the pattern of response of fibroblasts to the inhibition of DNA replication by BPDE-I.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1985

DNA repair and replication in human fibroblasts treated with (+/-)-r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene .

DNA repair and replication were examined in diploid human fibroblasts after treatment with (+/-)-r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE-I). Unscheduled DNA synthesis exhibited a linear response to BPDE-I concentrations up to 1.5 microM and a saturation plateau after higher concentrations. Maximal unscheduled DNA synthesis was observed in the first hour after treatment with synthesis diminishing progressively thereafter. Half-maximal unscheduled DNA synthesis was seen within 4-6 h after treatment with 0.7 microM BPDE-I. DNA replication was inhibited by BPDE-I in a dose- and time-dependent fashion. The mechanisms of this inhibition were characterized by velocity sedimentation of pulse-labeled nascent DNA in alkaline sucrose gradients. Very low concentrations of BPDE-I (0.03 and 0.07 microM) were found to inhibit replicon initiation by up to 50% within 30-60 min after treatment. Recovery of initiation following these low concentrations was evident within 3 h after treatment. Higher concentrations of carcinogen inhibited DNA synthesis in active replicons. This effect was manifested by a reduction in incorporation of precursor into replication intermediates of greater than 1 X 10(7) Da with the concurrent production of abnormally small nascent DNA. When viewed 45 min after treatment with 0.17 microM BPDE-I the combination of these two effects partially masked the inhibition of replicon initiation. However, even after treatment with 0.33 microM BPDE-I an effect on initiation was evident. These results reveal a pattern of response to BPDE-I that is quite similar to that produced by 254 nm radiation.

Benzopyrenes↗
PubMed1985

Transfer of plasmids pBR322 and pBR325 in wastewater from laboratory strains of Escherichia coli to bacteria indigenous to the waste disposal system.

Laboratory strains of Escherichia coli containing plasmid pBR325 (or pBR322) were coincubated with a mobilizer strain of E. coli (containing the conjugative plasmid R100-1) and a recipient strain of bacteria. Bacterial strains isolated from raw wastewater or a plasmid-free E. coli laboratory strain served as recipients. Transfer of the pBR plasmid into the recipient strain occurred during a 25-h coincubation in either L broth or sterilized wastewater; transfer frequencies were several orders of magnitude lower in wastewater. After the coincubation, recipients exhibited both plasmid-encoded phenotypic characteristics and an altered plasmid profile, as shown by agarose gel electrophoresis of purified plasmid DNA.

Conjugation, Genetic↗
PubMedDate not supplied

In vitro transcripts of turnip yellow mosaic virus encompassing a long 3' extension or produced from a full-length cDNA clone harbouring a 2 kb-long PCR-amplified segment are infectious.

Two types of full-length cDNA clones have been constructed corresponding to the entire genome of turnip yellow mosaic virus (TYMV), from which infectious transcripts devoid of 5' non-viral extensions can be synthesized in vitro. The first type of transcript (tTYFL7) harbours 75 non-viral nucleotides at its 3' end, whereas the second type (tTYFL84) possesses only 2 non-viral nucleotides at its 3' end. The 2 kilobase-long 3' region of tTYFL84 derives from amplification by the polymerase chain reaction of the corresponding TYMV cDNA. Both tTYFL7 and tTYFL84 are infectious in rapeseed protoplasts and plants. tTYFL7 is far less infectious than wild-type TYMV RNA and somewhat less infectious than tTYFL84. The possible effects of the 3' extraviral sequences of tTYFL7 and the heterogeneity observed in the infectivity of other transcripts prepared as was tTYFL84 are discussed.

Base Sequence↗
PubMedDate not supplied

Renal vascular Doppler imaging: clinical benefits of power mode.

Power Doppler ultrasound (US) is a new technology that is superior to conventional color Doppler imaging in the detection of blood flow. Because of its greater sensitivity to flow and reduced angle dependence, power Doppler US demonstrates optimal color filling of renal pedicular vessels and allows improved evaluation of the renal parenchymal microvasculature. Power Doppler US was used as an adjunct to conventional color Doppler imaging in technically challenging cases and to improve evaluation of renal vascular disorders in a series of 916 patients. The primary clinical advantages of using power Doppler US compared with conventional color Doppler imaging include better morphologic appreciation of atherosclerotic changes in the renal artery wall, allowing improved diagnostic performance especially in hemodynamically nonsignificant plaques; ability to differentiate between subocclusive renal artery stenosis and occlusion; increased confidence in the diagnosis of renal vein thrombosis and in the assessment of caval tumor thrombus; and better appreciation of renal cortical perfusion defects. In addition, because of its greater sensitivity to perivascular artifact, power Doppler US has the potential to increase the detection rate for intrarenal arteriovenous fistulas.

Arteriosclerosis↗
PubMedDate not supplied

[Biomarkers of tobacco smoke exposure].

Tobacco smoking is a major risk factor for cancer, cardiovascular diseases and respiratory illnesses. Smoking is increasing among children and adolescents with subsequent consequences on the health. Furthermore, maternal tobacco smoking during pregnancy adversely affects prenatal growth. Nicotine, the most important tobacco alkaloid, is responsible for maintaining tobacco addiction. According to a recent Circulaire de la direction générale de la santé, nicotine dependence should be determined through questionnaires and quantitative estimate of nicotine metabolites. Nicotine blood level fluctuates and urinary nicotine excretion is of short duration. Nicotine is intensively metabolized in the liver and oxidized into cotinine. Urinary measurement of cotinine appears to be highly related with the degree of intoxication and to allow the differentiation between non exposed and exposed non-smokers. In order to check the present application of nicotine metabolites measurement, a survey was conducted in 340 smoking cessation units. Forty percent physicians (n = 137) answered the survey. For 17% of them, the quantification of nicotine metabolites is included in their daily practise and for 79%, guidelines about cotinine measurement should be given in France. Sixty-seven biologists answered the survey. Recommendations for immunoassay and HPLC determination of cotinine should be given as reported by 66 and 44% of them respectively. Indeed, urinary cotinine measurement with high performance liquid chromatography is highly sensitive and specific. However, immunoassays are more convenient. These two approaches are presently under investigation in order to provide guidelines for optimal use in various clinical situations. Traditional measures for nicotine dependence are the number of cigarettes smoked per day, nicotine intake expressed as mg per day, Fagerstr m questionnaire, expired air carbon monoxide, thiocyanates and cotinine levels in biological fluids. Urinary cotinine measurement is the most useful for the follow-up of smoking cessation including adjustment of nicotine replacement therapy, especially after a clinical event or for the follow-up of smoking pregnant women. It allows the detection of passive smoke exposure in children who are hospitalized for recurrent respiratory illnesses.

Biomarkers↗