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C Guidi-Rontani

Publications and source records attributed to C Guidi-Rontani.

24 records · Page 2Linked to original sources
PubMed1985

RNA polymerase mutant able to express in vivo and in vitro the lactose operon in the absence of the cAMP-CRP complex.

By genetic analysis, we have localized a new mutation, isolated from rho-crp background, responsible for a carbohydrate-positive phenotype. The mutation maps in the rpoB gene coding for the beta-subunit of Escherichia coli RNA polymerase. Using reverse transcriptase analysis of transcripts obtained in vivo and transcription assays in vitro, we have shown that this altered RNA polymerase can efficiently initiate the transcription of the lactose operon in the absence of the cAMP-CRP complex both in vivo and in vitro.

Cyclic AMP↗
PubMed1984

Transcriptional control of polarity in Escherichia coli by cAMP.

In Escherichia coli, 3'5'-adenosine cyclic monophosphate (cAMP) and its receptor protein (CAP) are known to be involved in the control of transcription initiation of catabolic operons. In previous papers we have shown that the cAMP-CAP complex is also involved as a modulator of polarity in polycistronic transcription units. Furthermore we showed that there exists a functional relationship between this complex and the transcription termination protein, Rho. In this work, we measured mRNA synthesis corresponding to the promoter proximal and distal parts of the lac and gal operons by DNA-RNA hybridization. We show that in these operons the main polarity effect is essentially transcriptional and the cAMP-CAP complex decreases polarity by interfering with premature transcription termination.

Base Sequence↗
PubMed1981

Isolation and characterization of an Escherichia coli mutant affected in the regulation of adenylate cyclase.

A mutant, cyaR1, affecting regulation of adenylate cyclase expression or activity is described. It was obtained as a thermoresistant revertant of a strain harboring a thermosensitive transcription termination factor, rho (rho-15). This mutant failed to synthesize adenosine 3',5'-phosphate and exhibited a carbohydrate-negative phenotype. A secondary mutation at the crp locus (crpC) restored the ability of the mutant to synthesize adenosine 3',5'-phosphate, enabled the expression of catabolite-sensitive operons, and conferred on the strain an extreme sensitivity to catabolite repression. In addition, we showed that the crpC mutation restored the pleiotropic carbohydrate-positive phenotype even in a delta cya background. We interpret this to mean that the adenosine 3',5'-phosphate receptor protein regulates negatively either the activity or synthesis of adenylate cyclase and that the cyaR1 mutation is either in a regulatory protein or a regulatory site of adenylate cyclase.

Adenylyl Cyclases↗
PubMed1980

Catabolite repression in Escherichia coli mutants lacking cyclic AMP receptor protein.

Pleiotropic carbohydrate-positive pseudorevertants have been isolated from a specific class of rho-crp double mutants of Escherichia coli carrying both defective transcription termination protein, rho, and cyclic AMP receptor protein. The modulation of catabolite repression of beta-galactosidase, amylomaltase, and tryptophanase has been studied in the pseudorevertants. It has been found that these mutants exhibit catabolite repression. Because catabolite-sensitive operons can be expressed in the absence of functional cyclic AMP receptor protein, this would suggest on the one hand that the cyclic AMP-receptor protein complex is not the exclusive mediator of catabolite repression and on the other hand that rho might be involved in the regulation of catabolite-sensitive operons.

Cyclic AMP↗
PubMedDate not supplied

Contribution of plasminogen activator urokinase to in vitro cytotoxicity of diphtheria toxin.

Nicking of diphtheria toxin (DT), i.e. proteolytic cleavage at an arginine-rich region within the first disulphide loop, is a prerequisite to the intoxication process. We show that protease(s) required in this process was synthesized and secreted by the sensitive cells and that antibodies against plasminogen activator urokinase (uPA) decreased the in vitro cytotoxicity of DT on Vero cells. Our results demonstrate that uPA secreted by Vero cells cultured in vitro is one of the cellular proteases involved in the cleavage and activation of diphtheria toxin.

Antibodies↗