Isolation and characterization of SOS constitutive mutations in Escherichia coli.

Persistent Link:
http://hdl.handle.net/10150/184398
Title:
Isolation and characterization of SOS constitutive mutations in Escherichia coli.
Author:
Ossanna, Nina.
Issue Date:
1988
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Early events occurring during induction of the SOS response in Escherichia coli are poorly understood. In order to understand the early steps in SOS induction more fully, we have isolated several mutations which constitutively express the SOS regulon. Using a Mud(Apᴿ,lac) fusion to the SOS regulated gene sulA, we isolated Lac⁺ colonies as mutants in which RecA protein is constitutively activated for repressor cleavage. The mutations map to four loci: dam, lig, uvrD and recA. The extent of constitutive SOS induction in these mutants varied greatly, indicating different levels or types of signal in the cell. The mutations isolated demonstrate two early steps in SOS induction. The first step in SOS induction is signal generation and includes mutations found in dam, lig and uvrD genes. The mutant gene products presumably alter DNA metabolism to produce an inducing signal. These non-lethal mutations lead to sub-induction and probably generate very specific signals, such as abnormally unwound DNA in the case of DNA helicase II mutants or unsealed DNA nicks that result from deficient ligation in lig mutants. Greater induction may require quantitatively more signal or different types of signal generated by severe defects leading to cell death. These mutations also show that signal is a variable quantity, allowing the cell to fine tune the levels of SOS repair activity according to the amount or type of signal (damage) perceived. In some cases (such as dam mutations), blocking the SOS response by lexA(Ind⁻) alleles leads to cell death. In this type of constitutively activated strain, the increased level of repair from SOS induction is required to allow the cell to tolerate potentially lethal DNA structures generated by the mutant gene product. The second step in induction is the interaction of signal with RecA protein and is shown by isolating 8 recA mutants. Mutant recA alleles caused the strongest SOS induction in any mutants obtained, similar to the level found in strains lacking repressor (lexA(Def) mutants). This full induction in the absence of lethal DNA damage underscores the pivotal role of RecA protein in regulating the SOS response.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Escherichia coli -- Genetics.; Mutation (Biology); DNA damage.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Molecular and Cellular Biology; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Mount, David

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleIsolation and characterization of SOS constitutive mutations in Escherichia coli.en_US
dc.creatorOssanna, Nina.en_US
dc.contributor.authorOssanna, Nina.en_US
dc.date.issued1988en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractEarly events occurring during induction of the SOS response in Escherichia coli are poorly understood. In order to understand the early steps in SOS induction more fully, we have isolated several mutations which constitutively express the SOS regulon. Using a Mud(Apᴿ,lac) fusion to the SOS regulated gene sulA, we isolated Lac⁺ colonies as mutants in which RecA protein is constitutively activated for repressor cleavage. The mutations map to four loci: dam, lig, uvrD and recA. The extent of constitutive SOS induction in these mutants varied greatly, indicating different levels or types of signal in the cell. The mutations isolated demonstrate two early steps in SOS induction. The first step in SOS induction is signal generation and includes mutations found in dam, lig and uvrD genes. The mutant gene products presumably alter DNA metabolism to produce an inducing signal. These non-lethal mutations lead to sub-induction and probably generate very specific signals, such as abnormally unwound DNA in the case of DNA helicase II mutants or unsealed DNA nicks that result from deficient ligation in lig mutants. Greater induction may require quantitatively more signal or different types of signal generated by severe defects leading to cell death. These mutations also show that signal is a variable quantity, allowing the cell to fine tune the levels of SOS repair activity according to the amount or type of signal (damage) perceived. In some cases (such as dam mutations), blocking the SOS response by lexA(Ind⁻) alleles leads to cell death. In this type of constitutively activated strain, the increased level of repair from SOS induction is required to allow the cell to tolerate potentially lethal DNA structures generated by the mutant gene product. The second step in induction is the interaction of signal with RecA protein and is shown by isolating 8 recA mutants. Mutant recA alleles caused the strongest SOS induction in any mutants obtained, similar to the level found in strains lacking repressor (lexA(Def) mutants). This full induction in the absence of lethal DNA damage underscores the pivotal role of RecA protein in regulating the SOS response.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectEscherichia coli -- Genetics.en_US
dc.subjectMutation (Biology)en_US
dc.subjectDNA damage.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineMolecular and Cellular Biologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorMount, Daviden_US
dc.contributor.committeememberLittle, Johnen_US
dc.contributor.committeememberIto, Juneen_US
dc.contributor.committeememberHewlett, Martyen_US
dc.contributor.committeememberBrower, Dannyen_US
dc.identifier.proquest8814266en_US
dc.identifier.oclc701246826en_US
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