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Biomedical subjects

C Portier

Publications and source records attributed to C Portier.

At least 55 records · Page 3Linked to original sources
PubMed1986

Initiation, attenuation and RNase III processing of transcripts from the Escherichia coli operon encoding ribosomal protein S15 and polynucleotide phosphorylase.

The rpsO gene of Escherichia coli, which encodes ribosomal protein S15 is located at 69 minutes on the chromosome. It is adjacent to the pnp gene, which encodes polynucleotide phosphorylase. The two genes are separated by 249 nucleotides and are transcribed in the same direction. We report here in vivo S1 nuclease mapping and in vitro transcription experiments that demonstrate that rpsO and pnp are cotranscribed from a promoter P1, located 108 nucleotides upstream from rpsO, and that another promoter P2, located between the two genes 158 nucleotides upstream from pnp, also directs the transcription of pnp. Transcription from P1 can either terminate at the terminator t1 identified in vivo and in vitro, 18 nucleotides downstream from rpsO, or transcribe through t1 and into pnp. Comparison of the transcripts synthesized in wild-type and RNase III-deficient strains of E. coli shows that all the P1 readthrough transcripts and P2 transcripts are cleaved by RNase III. Two specific cuts are made by RNase III in a double-stranded structure about 100 nucleotides upstream rpsO. We also found that some transcripts of this operon start 47 nucleotides downstream from rpsO, in the region of t1. No promoter has been identified in this region. This mRNA is attributed to an endonucleolytic cleavage of the polycistronic transcripts and the location of the cut is named M. The order of the transcription signals and of the maturation sites in relation to rpsO and pnp can be summarized as follows: P1, rpsO, t1, M, P2, RNase III-processing sites, pnp. The possible roles of mRNA processing events in the expression of rpsO-pnp operon are discussed.

Endonucleases↗
PubMed1986

[Unruptured aneurysms of the sinus of Valsalva disclosed by syncopal disorders of cardiac excitability. Apropos of 2 cases].

Aneurysms of the sinus of Valsalva are rarely diagnosed before rupture into the cardiac cavities which usually leads to the appearance of a continuous murmur and cardiac failure. In the two cases described, the presenting symptom of the aneurysm was syncope due to cardiac hyperexcitability: ventricular tachycardia in the first and paroxysmal tachyarrhythmia in the second case. The presenting symptoms of unruptured aneurysms of the sinus of Valsalva were analysed. In general, they are: uncontinuous cardiac murmurs: either diastolic murmurs of aortic regurgitation, systolic murmurs of mitral or tricuspid regurgitation, or, as in our first case, of obstruction to right ventricular ejection; arrhythmias: the commonest are conduction defects, which can be syncopal; hyperexcitability (especially ventricular) seems to be very care. Echocardiography is a valuable tool for the diagnosis of sinus of Valsalva aneurysms. The appearances of unruptured aneurysms in our two patients are described. The presence of syncopal cardiac hyperexcitability, possibly associated with one of the preceding auscultatory abnormalities is an indication for echocardiography which may lead to the diagnosis of this condition.

Aged↗
PubMed1986

The impact of litter effects on dose-response modeling in teratology.

The fitting of dose-response models to teratology data involving littermates in order to generate estimates of teratogenic risk is receiving increasing attention as a potential alternative to the "safety-factor" approach to risk estimation. In this paper, we utilize the beta-binomial distribution to introduce varying degrees of intralitter correlation, and, for purposes of illustration, consider a logistic dose-response model that describes the logit of risk as a straight-line function of ln(dose). The biases and (exact and asymptotic) variances of the maximum likelihood estimators of the intercept and slope are studied by simulation as a function of the intralitter correlation structure.

Animals↗
PubMed1984

Expression of the rpsO and pnp genes: structural analysis of a DNA fragment carrying their control regions.

Precise physical mapping of the genes rpsO and pnp coding respectively for ribosomal protein S15 and polynucleotide phosphorylase together with regions involved in the regulation of their expression has been obtained by the analysis of in vitro deletion mutants. The results suggest that each gene has its own promotor, but that there is coexpression of rpsO and pnp. The nucleotide sequence of rpsO and of the beginning of pnp is presented and includes the presumed regulatory regions of these genes. Several features of the sequence support the mapping experiments and are discussed in relation to the expression of the ribosomal and pnp genes.

Chromosome Deletion↗
PubMed1983

Optimal design of the chronic animal bioassay.

Optimal experimental designs for carcinogenicity bioassays conducted for the assessment of risks associated with exposure to environmental chemicals are derived. For our purposes, an optimal experimental design is a design that minimizes the mean-squared error of the maximum likelihood estimate of the virtually safe dose from the Armitage-Doll multistage model and maintains a high power for the detection of increased carcinogenic response. Three- and four-dose designs (including control as one of the doses) are discussed for a variety of dose response patterns. Monte Carlo simulation techniques are used to estimate the power and mean-squared error for small samples sizes. Two forms of the multistage model are used to estimate the virtually safe dose: the linear model and the linear-quadratic model. The optimal designs for fitting the linear model used a control group and a group administered the maximum tolerated dose, with about 50% of the animals at each dose. The three- and four-dose optimal designs when fitting the linear-quadratic model were found to be equivalent. However, after considering several biological issues, including overt toxicity, the optimal four-dose designs would use between 150 and 300 animals, with 50 to 60 animals in the control group, and 40 to 60 animals in the group administered the maximum tolerated dose. One-third of the remaining animals would be administered a dose between 10 and 30% of the maximum tolerated dose, and two-thirds of the remaining animals would be administered 50% of the maximum tolerated dose.

Animals↗
PubMed1983

Low-dose-rate extrapolation using the multistage model.

The distribution of the maximum likelihood estimates of virtually safe levels of exposure to environmental chemicals is derived by using large-sample theory and Monte Carlo simulation according to the Armitage-Doll multistage model. Using historical dose-response we develop a set of 33 two-stage models upon which we base our conclusions. The large-sample distributions of the virtually safe dose are normal for cases in which the multistage-model parameters have nonzero expectation, and are skewed in other cases. The large-sample theory does not provide a good approximation of the distribution observed for small bioassays when Monte Carlo simulation is used. The constrained nature of the multistage-model parameters leads to bimodal distributions for small bioassays. The two modes are the direct result of estimating the linear parameter in the multistage model; the lower mode results from estimating this parameter to be nonzero, and the upper mode from estimating it to be zero. The results of this research emphasize the need for incorporation of the biological theory in the model-selection process.

Biological Assay↗
PubMed1981

Cloning of E. coli pnp gene from an episome.

Starting with an F' episome harboring a transposon inserted in the pnp gene (Portier 1980), we were able to identify an EcoRI restriction fragment carrying the pnp and argG genes. This fragment, from both wild-type and mutant episomes, was cloned ni pACYC184. The presence of argG on the fragment allowed positive selection of the desired clones in an auxotrophic strain (argG). A restriction map was established and a fragment of 3 megadaltons subcloned in the plasmid vector pBR322. The pnp gene corresponds to about 50% of this subcloned segment and was roughly located by deletion mapping. The direction of transcription and locations of the promotor and gene extremities were determined by analyzing proteins synthesized in "maxi-cells". In addition, the gene coding for a 10,000 dalton protein was found to reside adjacent to the beginning of the pnp structural gene. Strains carrying plasmids which express the pnp overproduce polynucleotide phosphorylase.

Arginine↗
PubMed1980

Isolation of a polynucleotide phosphorylase mutant using a kanamycin resistant determinant.

Insertion in an episome of a kanamycine-resistant element (Tn5) at the polynucleotide phosphorylase gene level, results, after transduction into a wild strain, by the loss of activities specific to polynucleotide phosphorylase. A low phosphorolytic activity is nevertheless detectable in crude extracts, but no longer in extracts slightly purified after heat treatment at 54 degrees C. The part played by other enzymes in these activities is discussed. Bacterial growth is not affected by introduction of the mutation.

Coliphages↗
PubMed1976

Study on the structure-function relationship of polynucleotide phosphorylase: model of a proteolytic degraded polynucleotide phosphorylase.

It is already known that modification of E. coli polynucleotide phosphorylase by endogenous proteolysis induces drastic changes in both phosphorolysis and polymerisation reactions. The structural parameters of the proteolysed polynucleotide phosphorylase are described. The phosphorolysis of polynucleotide, which is quite progressive for the native enzyme, is shown to be only partially progressive for the degraded enzyme, owing to the loss of polymer attachment sites.

Escherichia coli↗
PubMed1975

Quaternary structure of polynucleotide phosphorylase from Escherichia coli: evidence of a complex between two types of polypeptide chains.

A new form of polynucleotide phosphorylase containing alpha and beta subunits was isolated (form B) by purification without preparative electrophoresis; this form was compared to the enzyme obtained by preparative electrophoresis purification (form A). The Stokes radius of these two forms are very different: 6.4 nm for form A and 8.7 - 9.0 nm for form B; on the other hand the sedimentation coefficients are close: 8.9 S and 9.9 S respectively. Such a result suggests that form B is very asymmetric. The apparent molecular weights, calculated from the Stokes radii and from the sedimentation coefficients, are approximately 365000 for form B and 252000 for form A. The latter is homogeneous on polyacrylamide gel, whereas the former yields two components, one of which behaves similarly to form A. Finally, whereas form A is composed of only one type of subunit, alpha, form B contains two types of chains: alpha (Mr 86000 +/- 5000) and beta (Mr 48000 +/- 2000) in stoichiometric proportions. From these results we believe that one should assume for form B the existence of a complex between form A and beta chains; the role of the latter still remains to be specified.

Binding Sites↗
PubMed1975

[Analysis of a small quatity of polypeptides by two-dimensional electrophoresis: application to characterization of proteins].

A new two-dimensional electrophoresis is described. The first electrophoresis is performed in a 10 p. cent gel (1 X 110 mm) in the presence of 7 M urea; the migration in the second dimension proceeds on a 20 p. cent polyacrylamide sheet (160 X 110 X 1 mm) in the presence of sodium dodecyl sulphate. This system resolves most of the polypeptides obtained by treating a very small amount (about 100 mug) of proteins with cyanogene bromide. Macromolecules can thus be quickly and easily characterized.

Alkaline Phosphatase↗
PubMed1975

[Quaternary structure of Escherichia coli polynucleotide phosphorylase: chemical characterization of form A].

We had previously shown the existence of two classes of polynucleotide phosphorylases : Form A which is made of alpha chains and carries the catalytic sites ; and form B which is constituted of alpha chains and of beta chains. We performed some chemical analyses of form A (N-terminal sequence, amino acid composition, peptide mapping) which suggest that the alpha chains are all identical and moreover that they have no relationship with the beta chains. The latter do not therefore derive from a partial proteolytic degradation of the alpha chains and can therefore be considered as true subunits of the enzyme.

Amino Acid Sequence↗