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M Dreyfus

Publications and source records attributed to M Dreyfus.

At least 19 recordsLinked to original sources
PubMed1992

Interdependence of translation, transcription and mRNA degradation in the lacZ gene.

We have constructed a collection of Escherichia coli strains which differ by point mutations in the ribosome binding site (RBS) that drives the translation of the lacZ gene. These mutations affect the Shine-Dalgarno sequence or the initiation codon, or create secondary structures that sequester these elements, and result in a 200-fold variation in beta-galactosidase expression. Surprisingly, these variations of expression are paralleled by nearly equivalent changes in the lacZ mRNA level. The ratio of the beta-galactosidase expression to the mRNA level reflects the average spacing between translating ribosomes: hence, paradoxically, mutations that affect translation initiation do not correspondingly change this spacing. Further analysis of the mRNA level variations shows that they originate from two independent mechanisms. When beta-galactosidase expression exceeds a threshold corresponding roughly to one translation event per transcript, the variations in the efficiency of translation initiation affect largely the chemical and functional lifetimes of the mRNA. We further show that the rate-limiting step in the chemical decay process is an RNase E-dependent cleavage, which is outcompeted by translation initiation. Below this expression threshold, the mRNA lifetime levels out and strain-to-strain variations in mRNA level arise solely from polarity effects. We suggest that, in this activity range, most mRNA molecules that escape polarity are crossed by a single ribosome, and hence are identical from the viewpoint of degradation. Altogether, the tight couplings between translation initiation on one hand, polarity and/or mRNA degradation on the other, result in translation initiation events being closely spaced in time even from inefficient RBS, at the expense of the mRNA level. Finally, we evocate the possible beneficial consequences of a coupling between translation, transcription and mRNA degradation, for the management of cellular resources.

Base Sequence↗
PubMed1992

Culture conditions differentially affect the translation of individual Escherichia coli mRNAs.

Our aim is to investigate whether changes in growth conditions can differentially affect the initiation of translation from individual Escherichia coli mRNAs that are not subjected to specific translational control. As a model system, we have constructed a series of point-mutated lacZ genes which differ in their Shine-Dalgarno (SD) sequence, their initiator codon, or the secondary structure around these elements. Alterations in growth conditions produced large (up to 8-fold) changes in the relative expression from these genes, which, we argue, stem from changes in their relative efficiencies of translation initiation. In particular, compared to genes bearing mutations outside the SD or initiator codon, genes mutated in these elements experience a significant decrease in their expression when cells are grown in minimal rather than rich medium; at 42 degrees C rather than 37 degrees C; or under amino acid starvation. We discuss the mechanisms underlying these effects, and evocate their possible generality.

Base Sequence↗
PubMed1992

Bacteriophage T7 RNA polymerase travels far ahead of ribosomes in vivo.

We show that in Escherichia coli at 32 degrees C, the T7 RNA polymerase travels over the lacZ gene about eightfold faster than ribosomes travel over the corresponding mRNA. We discuss how the T7 phage might exploit this high rate in its growth optimization strategy and how it obviates the possible drawbacks of uncoupling transcription from translation.

Base Sequence↗
PubMed1992

Differentiation-controlled synthesis and binding of thrombospondin to granulosa cells.

Thrombospondin (TSP) is a large glycoprotein, synthesized by several matrix-forming cells and incorporated into their extracellular matrix. In several cell types its presence supports cell growth and proliferation. To investigate the role of this protein in cell differentiation, we studied the hormonal effect of TSP production and receptor-mediated binding to primary granulosa cells prepared from diethylstilbestrol-treated immature female rats. These cells can be induced to differentiate by FSH, 8-bromo-cAMP (8-Br-cAMP), or forskolin. Progesterone production is induced during differentiation, and its level of synthesis is an important manifestation of the differentiated phenotype. We find that undifferentiated granulosa cells synthesize and secrete TSP. The protein comprises about 0.5% of the total cell protein, and it is the major protein secreted in culture. Treatment of the cells with FSH or 8-Br-cAMP reduces TSP production dramatically, and forskolin completely inhibits it. In parallel, we observed that the undifferentiated cells bind TSP specifically with a Kd of 1.8 nM, and the number of binding sites per cell is 1.7 x 10(5). This binding can be prevented by excess TSP or an anti-TSP monoclonal antibody (B7-3). This ability to bind TSP is completely lost after induction of differentiation by FSH or 8-Br-cAMP. Our findings show that both the production and binding of TSP to granulosa cells are tightly controlled by normal cell differentiation and indicate that changes in TSP are correlated with the passage of the cell through the stages of maturation, a passage that also involves changes in cell shape and extracellular interactions and in the steroidogenic capacity of these cells.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1992

[Role of herpes virus simplex and cytomegalovirus as cofactors of papillomavirus in dysplastic and cancerous lesions of the uterine cervix].

Human papillomaviruses (HPV) play an important role in cervical carcinogenesis but are probably not the only factors. To assess the role of HPV 6 and 11, of herpes simplex virus (HSV) and of cytomegalovirus (CMV) as cofactors for HPV 16 and HPV 18, we used polymerase chain reaction (PCR). The genomes of these six viruses was searched for in cervical biopsies, inbred in paraffin, from 22 normal cervices, 21 low grade cervical intraepithelial neoplasia (CIN), 21 high grade CIN and 20 squamous cancers. HPV 16 DNA had the highest prevalence in cervical lesions. Its frequency reached 24% in low grade CIN, 57% in high grade CIN, 50% in cancers and 9% in normal cervices. The simultaneous presence of HPV 16 and/or HPV 18 DNA and CMV and/or HSV DNA was significantly more frequent in high grade CIN and cancers than in normal cervices. On the other hand the presence of HPV 16 and/or HPV 18 DNA in samples lacking the other viral genomes did not significantly differ between the groups. Consequently the disease-viral infection relation was not apparent when these two "potentially oncogenic" HPV are isolated without coinfection by HSV or CMV. Our results are in agreement with the hypothesis of the role of herpesviruses as cofactors in cervical carcinogenesis. These viruses may disturb the control mechanisms of cellular growth and differentiation in HPV infected cells.

Adult↗
PubMed1991

In the Escherichia coli lacZ gene the spacing between the translating ribosomes is insensitive to the efficiency of translation initiation.

We have constructed a series of 44 Escherichia coli strains in which the chromosomal region corresponding to the Ribosome Binding Site (RBS) of the lacZ gene, has been replaced by small DNA fragments harboring either RBSs from other genes, or artificial RBSs. The beta-galactosidase expression from these strains ranges from 1 to 130 per cent of that of the parental strain. Using this collection, we demonstrate here that strain-to-strain variations in expression are paralleled by nearly equivalent variations in lacZ mRNA content. We propose that, in this system, polarity and mRNA stability are tightly coupled to translation initiation, so that changes in RBS efficiency are detected mainly as changes in mRNA concentration rather than in the spacing between translating ribosomes. In addition, we show that the mRNA sequence immediately downstream from the initiator codon influences per se the lifetime of the lacZ mRNA. We discuss the mechanism of the interdependence between translation, transcription and degradation in this gene, and speculate about the general role of this interdependence in determining the expression of bacterial genes.

Acetylglucosaminidase↗
PubMed1991

[Recurrent thrombocytopenic thrombotic purpura associated to prostatic cancer. A case].

The association between thrombocytopenic thrombotic purpura (TTP) and infectious or multisystem disease, pregnancy, transplantation, drugs and toxins is well known. The onset of TTP in the course of neoplasm is rarely described. The authors report one case of TTP associated with prostatic tumor. TTP preceded the discovery of neoplasm by 12 months. Moreover, TTP showed an original course with four recurrences despite antiplatelet and hormonal therapies; the successive regressions were obtained with less and less effort, as TTP was discovered at an early stage.

Humans↗
PubMed1991

The relation between translation and mRNA degradation in the lacZ gene.

The technique of gene fusion, in which the gene of interest, severed from its 3' end, is in-phase fused to a reporter gene--usually lacZ--is widely used to study translational regulation in Escherichia coli. Implicit in these approaches is the assumption that the activity of the ribosome binding site (RBS) fused in-phase with lacZ, does not per se modify the steady-state level of the lacZ mRNA. Herein, we have tested this hypothesis, using a model system in which the RBS of the lamB gene is fused to lacZ. Several point mutations affecting translation initiation have been formerly characterized in this RBS, and we used Northern blots to study their effect upon the lacZ mRNA pattern. Two series of constructs were assayed: in the first one, a 51-bp fragment centered around the lamB initiator codon, was inserted in front of lacZ within the natural lactose operon, whereas in the second the lacZ gene was fused to the genuine malK-lamB operon just downstream from the lamB RBS. We observed that in the first series, the concentration and average molecular weight of the lacZ mRNA dropped sharply as the efficiency of the RBS decreased. This apparently arose from a decreased stability of the message, since the mRNA patterns are equalized when the endonuclease RNase E is inactivated. We suggest that in this case the rate limiting step in the decay process is an RNase E cleavage that is outcompeted by translation.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1991

[Colposcopy of the vulva].

A detailed colposcopy study of the cervix, vagina and vulva was conducted in 365 women referred for genital human papillomavirus (HPV) lesions, abnormal cervico-vaginal smear or cervical intraepithelial neoplasia (CIN). Valvuloscopic abnormalities, all biopsied, were found in 144 women, i.e. 40% of the population studied. Five types of vulvoscopic abnormalities are described: diffuse acidophilia (55% of abnormalities), acidophilic maculae (17%), micropapillae (20%), papulae (4%) and leucoparakeratosis (4%). Histological examination of the biopsy specimens obtained from 144 women with abnormal vulvoscopy showed 55 typical flat condylomas (38%), 50 probable flat condylomas (35%) and no signs of condyloma in 38 cases (27%). It also revealed the presence of four vulvar intraepithelial neoplasias (VIN) stages 2-3, all of them associated with typical or probable condyloma. Comparison between the 144 abnormal vulvoscopies and a series of 14 normal vulvoscopies made it possible to establish a significant correlation between the presence of valvuloscopic abnormalities and the finding of histological signs of typical or probable flat condyloma. The vulvoscopic images of subclinical vulvar HPV infection, but apart from papulae and, to a lesser extent, leucoparakeratosis, correlations between vulvoscopic and histological images were imprecise.

Acetates↗
PubMed1990

Transcription of single-copy hybrid lacZ genes by T7 RNA polymerase in Escherichia coli: mRNA synthesis and degradation can be uncoupled from translation.

In Escherichia coli transcription of individual genes generally requires concomitant translation, and thus the decay of mRNAs cannot be studied without the complication of translation. Here we have used T7 RNA polymerase to transcribe in vivo lacZ genes carrying ribosome binding sites of variable efficiency. We show that neither cell viability nor growth rate is affected by the T7-driven transcription of these genes, provided that they are present as single chromosomal copy. Furthermore, transcription is now completely uncoupled from translation, allowing large amounts of even completely untranslated mRNAs to be synthesized. Taking advantage of these features, we discuss the influence of the frequency of translation upon the processing and degradation of the lac message.

Binding Sites↗
PubMed1990

Translation initiation in Escherichia coli: old and new questions.

We discuss the features of Escherichia coli mRNAs which determine where and how efficiently translation is initiated. We have shown that DNA fragments comprising 60-80 nucleotides that bracket the initiation codon of real genes generally promote translation when inserted within a foreign mRNA, while those not corresponding to an authentic gene start do not do so even if they include a Shine-Dalgarno-like element followed by AUG or GUG. Therefore, the information that pinpoints the correct start sites, while extending beyond the mere presence of these elements, remains essentially local. The possible nature of this information is discussed. Next, we point out that, in order to remain accessible, translational starts must escape long-range base-pairing within large mRNAs, and we argue that the tight coupling between translation and transcription plays an important role in achieving this. Finally, we discuss two intriguing situations in which the initiation frequency should be dependent upon the rate of translation elongation.

Codon↗
PubMed1989

Regulatory elements involved in the bidirectional activity of an immunoglobulin promoter.

We show that the promoter from the mouse VH441 heavy-chain immunoglobulin gene, when present on plasmids transiently introduced into myeloma cells, promotes transcription bidirectionally, due to the presence on both strands of TATA-like sequences bracketing the highly conserved decanucleotide element. The two divergent promoters compete for the transcriptional machinery, their relative strength ultimately reflecting the likeness of the two TATA boxes to the consensus sequence. Moreover, their relative activity is also strongly influenced by certain point mutations within the distally located heavy-chain enhancer. The bearing of these results on current concepts of promoter function is discussed.

Animals↗
PubMed1989

[Adenomas of the liver and oral contraception. Clinical and therapeutic aspects apropos of a giant adenoma].

The first cases of benign liver tumors following estroprogestative therapy were described in 1973. Since that time, this relation between cause and effect has been demonstrated. The authors report the case of a giant liver adenoma which developed after 13 years of uninterrupted use of oral contraceptives. The advantage of this disease is not so much its prevalence which is low, but its clinical diagnosis. In fact, failure to recognize this entity may result in dramatic complications such as haemorrhagic rupture of the liver. The therapeutic approaches, whether wait-and-see or aggressive, all present a common objective: permanent discontinuance of estroprogestative drugs.

Adult↗
PubMed1989

Renin-promoter SV40 large T-antigen transgenes induce tumors irrespective of normal cellular expression of renin genes.

Chimeric genes containing the 5'-flanking regions of the mouse renin genes, Ren1 and Ren2, associated with the early region of the simian virus 40 (SV40) were constructed. The two recombinant genes which contain, respectively, 0.45- and 2.5-kb the Ren1 and Ren2 5'-flanking sequences, named Ren1Tag and Ren2Tag, were microinjected into fertilized eggs. Tumors arose after a latency of 5-9 months in mouse lines harboring these hybrid genes except for one, in which a different and earlier pathology was observed (peripheral neuropathies). Most of the pathologies developed by these transgenic mice reflect the tumorigenic spectrum of the SV40 early region gene (choroid plexus, kidney, intestinal tumors, and peripheral neuropathies). None of these tumors arose from renin-producing cells nor produced renin. As suggested by the tumor pathology, the expression of the SV40 large T-antigen did not follow the normal expression of the Ren1 and the Ren2 genes since SV40 large T-antigen mRNA was found in tissues which normally do not express renin.

Animals↗