RESUMO
recA protein (RecA) performs diverse catalytic activities that require a complex with single-stranded DNA and an NTP. A subset of these functions shows optimal activity at a high DNA/protein ratio and requires NTP hydrolysis, whereas other catalytic activities are optimal in RecA-saturated complexes that require NTP, but do not hydrolyze it. To analyze the mechanism of catalytic discrimination, we investigated the properties of RecA bound to small oligonucleotides (oligos) of defined sizes. We show that RecA bound to (dT)(16) is optimal for co-protease activity and not active as ATPase whereas the complex with (dT)(24) is competent in ATP hydrolysis but impaired as a co-protease. Thermodynamic measurements of the equilibrium-binding properties of these complexes showed that (dT)(24) promoted a more salt sensitive complex than the one formed with (dT)(16), indicating more ionic interactions between RecA and DNA in the former. X-ray pictures show that the oligo complexes form helixes. We propose that RecA may change its conformation as a function of the number of phosphates available to the monomer in the interacting DNA lattice, thus promoting an allosteric change in catalytic activities. This model offers explanations for the observed inhibition of co-protease activity by excess ssDNA.
Assuntos
DNA de Cadeia Simples/química , DNA de Cadeia Simples/metabolismo , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Recombinases Rec A/metabolismo , Regulação Alostérica/genética , Catálise , Microscopia Crioeletrônica , DNA de Cadeia Simples/genética , Proteínas de Escherichia coli/genética , Ligantes , Modelos Químicos , Oligonucleotídeos/genética , Oligonucleotídeos/metabolismo , Fosfatos/química , Fosfatos/metabolismo , Ligação Proteica/genética , Conformação Proteica , Recombinases Rec A/antagonistas & inibidores , Recombinases Rec A/genéticaRESUMO
Damage to the genome is unavoidable in living creatures, because of sunlight exposure as well as environmental chemicals present in food and drinking water. There is a need to monitor and purify the drinking water; therefore, several methods of detection have been developed. A very promising model system for this purpose is the zebrafish (Danio rerio), which is endowed with special qualities for detecting external as well as internal abnormalities. Grossman and Wei's assay [Grossman L, Wei Q (1995) Clin Chem 12:1854-1863], which measures the expression level of a nonreplicating recombinant plasmid DNA containing a UV-damaged luciferase reporter gene, shows that zebrafish can repair chromosomal lesions to a much greater extent than the human population. This vertebrate model is still very promising after possible down-regulation of the DNA repair enzymes.
Assuntos
Reparo do DNA , Peixe-Zebra/genética , Animais , PlasmídeosRESUMO
El embarazo no deseado en adolescentes es un problema de creciente actualidad con implicancias médicas y sicosociales. Se entrevistaron 295 adolescentes embarazadas del consultorio de ginecología infantojuvenil de la 1º Catédra de Ginecología de la U.B.A. Se analizaron las características médicas de estas gestaciones, las motivaciones psicológicas que las originaron y sus consecuencias sociales. En base a estos resultados se diferencian los grupos de alto riesgo y se dan pautas metodológicas para el médico que enfrenta esta situación (AU)
Assuntos
Gravidez , Adolescente , Humanos , Feminino , Gravidez não Desejada , Gravidez na AdolescênciaRESUMO
El embarazo no deseado en adolescentes es un problema de creciente actualidad con implicancias médicas y sicosociales. Se entrevistaron 295 adolescentes embarazadas del consultorio de ginecología infantojuvenil de la 1§ Catédra de Ginecología de la U.B.A. Se analizaron las características médicas de estas gestaciones, las motivaciones psicológicas que las originaron y sus consecuencias sociales. En base a estos resultados se diferencian los grupos de alto riesgo y se dan pautas metodológicas para el médico que enfrenta esta situación