The role of lambda CI cooperativity in the maintenance of the lysogenic state and the switch from lysogenic to lytic growth
AuthorWatson, Andrea Christine
AdvisorLittle, John W.
MetadataShow full item record
PublisherThe University of Arizona.
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.
AbstractUntil now, CI tetramer cooperativity has been theorized to be critical for the wild type behavior of λ. Specifically, it was believed that a CI cooperativity mutant phage would not be able to grow lysogenically. Further, if it could be altered in some way to grow lysogenically, it was thought that the lysogen would not have the ability to switch to and/or complete lytic growth after induction. However, the work on which these theories were based was done with uncoupled systems. Then, inferences were drawn as to the role cooperativity played in the intact switch. While this research was groundbreaking, CI levels were unregulated since the regulatory network was disconnected from the action of CI. This is unrealistic since within the lysogen, CI levels are extensively coupled to CI activity via feedback. In this work, I study the role of CI tetramer cooperativity in an intact phage. In this way, CI levels remain coupled to the extensive regulation which controls them. The CI level is regulated by its own activity. To test the role of CI cooperativity in λ physiology, specifically in the genetic switch, three CI cooperativity deficient phage were made. None could form stable, single lysogens. Therefore, the CI Y210X mutations were combined with mutations in the O(R) region that should confer increased occupancy of O(R)2, allowing stable lysogeny. A CI cooperativity deficient phage was isolated that could successfully complete all three aspects of λ physiology: lytic growth, lysogenic growth, and a threshold response to the switch between the two. Therefore, CI cooperativity is not required for wild type λ physiology. In addition, a CI Y210F phage was isolated. CI Y210F has wild type cooperativity. However, phenylalanine cannot make the contacts described in the CI structure papers, indicating that the proposed details of the cooperativity contacts shown in the papers are likely to be unnecessary or possibly incorrect.
Degree ProgramGraduate College
Molecular and Cellular Biology