published_or_final_version / abstract / toc / Ecology and Biodiversity / Master / Master of Philosophy

published_or_final_version / abstract / toc / Paediatrics and Adolescent Medicine / Doctoral / Doctor of Philosophy

published_or_final_version / Molecular Biology / Master / Master of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

No description available.

When the DNA of Escherichia coli is damaged a set of events termed "SOS functions" occur to aid cellular survival. The recA and lexA proteins are involved in the regulation of these functions. To determine the role of the lexA protein, amber mutations, designated spr-55(amber), were isolated in the lexA-3 gene. The lack of the lexA-3 gene product abolished sensitivity to ultraviolet light and resulted in the constitutive synthesis of recA protein. Introduction of amber suppressor mutations restored the original lexA-3 phenotype. It was concluded that spr mutations inactivate lexA protein resulting in the constitutive expression of the SOS functions. These data provide evidence that the lexA protein is the repressor for the recA gene. The repair of phage lambda (λ⁺) by ultraviolet light was determined in the strains carrying alleles of the spr, uvrA, and recA genes. The survival of the phage was more in the spr-51 uvrA⁺ strain as compared to wild type. These results were not dependent on the recA genotype. Introduction of the uvrA-6 mutation into the spr-51 uvrA⁺ recA⁺ strains resulted in the same relative decrease of phage survival. These results suggest that lexA protein is involved in the regulation of uvrA-dependent excision repair and that inactivation of lexA leads to the constitutive expression of excision repair. New mutant forms of lexaA protein were isolated. The lexA⁺, lexA-3, lexA-10, and lexA-27 proteins displayed identical mobilities in the Weber and Osborn gel system. The lexA-10 and lexA-27 genes showed different phenotypes and encoded proteins of different mobilities in the Laemmli gel system. It was concluded that the differences in mobilities observed in the Laemmli gel system are due to alterations in charge or amino acid, not in size; furthermore; the molecular weight of lexA⁺ protein was determined to be 24 kilodaltons.

No description available.

No description available.

Información extraída del <a href="http://www.cindefi.org.ar/?page_id=61&language=es">sitio web del CINDEFI</a>

Se comprueba que en las enteritis de los cerdos de la Provincia de Buenos Aires actúan indistintamente microorganismos solos o asociados. De 172 muestras bacteriológicas de necropsias y casos clínicos de enteritis de cerdos se aislaron: Escherichia coli 139; Salmonella 15; Proteus 10; Klebsiella 21; Sighella 2; Serratia 1; Pseudomonas 1; Campylobacter 28; Treponema 29 y Clostridum perfrigens 2. De las 139 cepas de E.coli un alto porcentaje correspondieron a los tipos somáticos 0149,0141,0138, y 08. Con los tipos somáticos 09,0141 y 04-0123 se reproduce experimentalmente la enfermedad de los edemas. Se detecta una elevada resistencia a las drogas con las cepas de E. coli aisladas en diferentes desórdenes entéricos, especialmente con los antibióticos de uso común en terapéutica veterinaria de nuestro país. Los serotipos más frecuentes de Salmonellas aisladas corresponden a S.cholera suis y S.tiphymurium. Treponema sp. y Campylobacter son los agentes bacterianos más comunmente aislados en la Disentería porcina. Se aisla C.perfrigens en 2 casos de enteritis necrótica. / The present work proved that pig enteritis in de province of Buenos Aires are caused by several kinds of microorganism that can act alone or associated in the gut. In a survey of 172 bacteriological samples taken from necropsied pigs with clinical sing of diarrhoea the following bacterias were isolated: E. coli 139;Salmonella 15;Proteus 10;Klebsiella 21;Sighella 2;Serratia 1;Pseudomonas 1;Campylobacter 28;Treponema 29 y Clostridium perfrigens 2. From the 139 strains de E.coli a high rate belonged to the somatic types 0149,0141,0138 y 08. With the somatic types of E.coli 09,0141 y 04-0123 the experimental reproduction of the Odenema disease was done. The strains of E.coli isolated from enteric disease showed high resistence specialy to the antibiotics of common use in the veterinary practice in Argentina. Within the Salmonella group.S.cholera suis and S.tiphimurium were the serotype isolated more frecuently. From pigs with pathological diagnosis of Swine Disentery,Traeponema and Campylobacter sp were isolated and from two cases of Necrotic a Clostridium perfrigens was recovery.