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Biomedical subjects

H Ponta

Publications and source records attributed to H Ponta.

At least 127 records · Page 7Linked to original sources
PubMed1979

Radiation sensitivity of messenger RNA.

Messenger RNA function is inactivated by irradiation with ultraviolet light. A unit length mRNA (in bases) is 2-3 times more sensitive than a unit length of DNA (in base pairs) with respect to the inactivation of template function. These data stem from four experimental systems all of which do not repair DNA: the translation of E. coli mRNA in rifampicin-treated cells, of T7 mRNA in infected E. coli, of f2 phage RNA in vivo, and of stable mRNA in chromosomeless minicells. The comparison of relative sensitivities to UV is relevant to the technique of UV mapping of transcription units which enjoys increasing popularity in pro- and eukaryotic genetic research.

DNA, Bacterial↗
PubMed1977

Development of Escherichia coli virus T1: repression of host gene expression.

Host protein synthesis, measured either as amino acid incorporation into proteins or as enzyme synthesis, is inhibited rapidly after infection Escherichia coli with T1. Analysis of this inhibition, using a technique which distinguishes between translation and transcription, revealed that translation of host mRNA is specifically blocked. Comparison of the time course of T1-induced host repression with inhibition by the drugs rifampicin, nitrofurantoin and chloramphenicol showed that T1 affects the initiation step of host translation. Intact membranes are apparently essential for host repression, suggesting a membrane-mediated process. Concomitant viral protein synthesis is not required. The membrane-altering principle is a constituent of the viral particle.

Bacterial Proteins↗
PubMed1977

Gene expression in mitochondria and bacteria.

Mitochondria and bacteria possess protein synthesizing machineries which are similar in many respects; The regulation of gene expression in mitochondria is unknown. We, therefore, tried to use a well-established prokaryotic regulatory system for the exploration of mitochondrial gene regulation. DNA of the bacterial virus can be used as a template for gene expression in a mitochondrial in vitro system. The gene directed enzyme synthesis in the mitochondrial system is the basis for a study of regulation in mitochondrial protein synthesis.

Chloramphenicol↗
PubMed1977

Development of E.coli virus T1: the pattern of gene expression.

T1 infected bacteria exhibit a distinct pattern of gene expression. The control of this expression is accessible to biochemical analysis. T1 induces the synthesis of 31 proteins in E. coli. The virion contains 15 proteins. By means of T1 amber mutants, 10 gene products have been assigned to specific T1 genes. Three classes of T1 proteins are defined by the kinetics of their syntheses: early, early-late and late proteins. The regulation of protein synthesis involes at least three mechanisms: for cessation of host gene expression, for discontinuation of the early class during the late phase and for induction of the late T1 proteins. The positive control of late gene expression is not coupled to replication. The host RNA-polymerase transcribes the viral genome throughout the infectious cycle. No virus coded RNA-polymerase is induced.

Bacterial Proteins↗
PubMed1976

A virus-specified mechanism for the prevention of multiple infection--T7- and T3-mutual and superinfection exclusion.

Co- and superinfection of cells with T3/T7 result in exclusion (mutual or superinfection exclusion). The exclusion mechanism is also directed against homologous (or identical) virus. Exclusion is established after the adsorption but before the genome becomes available for gene expression or replication, that is only one virus per cell develops. The exclusion is triggered by a constituant of the viral particle. An early T7 gene (M gene) (Schweiger et al., 1975) is essential for the formation of exclusion competent virions.

Bacterial Proteins↗
PubMed1976

E. coli membranes become permeable to ions following T7-virus-infection.

Infection of E. coli with the viruses T7 or T3 leads to a dramatic efflux of potassium ions. This ion efflux is caused by the virus particle since no concomitant protein synthesis is required. T7 mutants carrying deletions in the M-gene (Schweiger et al., 1975), however, yield virus particles disturbed in the ion release.

Biological Transport↗
PubMed1975

The sex-factor-dependent exclusion of coli virus T7.

The cause of T7 exclusion by the F episome was investigated. Extracts from neither normal nor infected F+ cells contained an inhibitor of gene expression in vitro. The protein synthesizing systems prepared in vitro from these cells supported T7 early and late protein synthesis with normal efficiency. The content of translational initiation factors in F- and F+ cells, both noninfected and infected, was almost identical. The episome-dependent block of T7 gene expression was observed only in intact cells and detailed kinetics of gene expression in vivo revealed a stop of all transcription and translation at or just before 11 min after T7 infection. The mechanism of F+-dependent T7 exclusion involves both episomal and viral gene products. The data indicate that a T7-induced membrane alteration of the F+ cell membrane leads to cessation of T7 development as well as to the death of the host cell ('suicide').

Cell Survival↗
PubMed1975

Protein kinase of bacteriophage T7. 1. Purification.

A protein kinase, ATP:protein phosphotransferase (EC 2.7.1.37) was detected in Escherichia coli after infection with bacteriophage T7. The enzyme was purified from the ribosomal wash fraction by conventional methods, affinity chromatography on Cibacron blue and on lysozyme coupled to Sepharose, and by cellogel electrophoresis. An approximately 5000-fold purification was achieved.

Chromatography, Affinity↗
PubMed1975

Protein kinase of bacteriophage T7. 2. Properties, enzyme synthesis in vitro and regulation of enzyme synthesis and activity in vivo.

Protein kinase, which was isolated from cells infected with T7, is indeed a viral gene product. This is shown by DNA-dependent synthesis in vitro. The protein kinase transfers phosphate from ATP to seryl or threonyl residues in protein. The enzyme has only a relative requirement for magnesium ions, but is only active at low ionic strength. The best substrate is lysozyme. T7 protein kinase activity is not stimulated by cyclic 3':5'-AMP and/or cyclic 3':5'-GMP. The T7 protein kinase carries -- SH groups essential for activity. There is indication that the enzyme phosphorylates itself and causes self inactivation, which may explain the fast disappearance of enzyme activity in vivo. Bacteriophage T3 also induces a protein kinase which is similar to the T7-induced enzyme in all respects tested.

Ammonium Chloride↗
PubMed1975

Transcriptional units for ribosomal proteins of Escherichia coli.

Transcriptional units for ribosomal proteins in Escherichia coli were measured using the ultraviolet sensitivities of the rates of synthesis of individual ribosomal proteins. The ultraviolet sensitivities of gene transcriptions are proportional to the distances from the promoters. The longest transcriptional units for ribosomal proteins are 3.6 x 10(6) of DNA molecular weight corresponding to 1.8 x 10(6) of RNA or to 180 000 of protein. The length would cover 10--12 genes of ribosomal proteins (of an average Mr of 15000-18000).

Bacterial Proteins↗
PubMed1975

In vivo and in vitro phosphorylation of DNA-dependent RNA polymerase of Escherichia coli by bacteriophage-T7-induced protein kinase.

After infection with bacteriophage T7 the beta' and to a lesser extent the beta subunits of E. coli DNA-dependent RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) are phosphorylated by a phage-gene-encoded protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37). The phosphorylation occurs on threonine residues and appears site-specific. It is probably the molecular basis of the early transcriptional control.

Coliphages↗