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Organization and function of the phage Lambda chromosome

Citation

Parkinson, John S. (1970) Organization and function of the phage Lambda chromosome. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/V4T1-KJ37. https://resolver.caltech.edu/CaltechTHESIS:08112015-161712404

Abstract

The process of prophage integration by phage λ and the function and structure of the chromosomal elements required for λ integration have been studied with the use of λ deletion mutants. Since attφ, the substrate of the integration enzymes, is not essential for λ growth, and since attφ resides in a portion of the λ chromosome which is not necessary for vegetative growth, viable λ deletion mutants were isolated and examined to dissect the structure of attφ.

Deletion mutants were selected from wild type populations by treating the phage under conditions where phage are inactivated at a rate dependent on the DNA content of the particles. A number of deletion mutants were obtained in this way, and many of these mutants proved to have defects in integration. These defects were defined by analyzing the properties of Int-promoted recombination in these att mutants.

The types of mutants found and their properties indicated that attφ has three components: a cross-over point which is bordered on either side by recognition elements whose sequence is specifically required for normal integration. The interactions of the recognition elements in Int-promoted recombination between att mutants was examined and proved to be quite complex. In general, however, it appears that the λ integration system can function with a diverse array of mutant att sites.

The structure of attφ was examined by comparing the genetic properties of various att mutants with their location in the λ chromosome. To map these mutants, the techniques of heteroduplex DNA formation and electron microscopy were employed. It was found that integration cross-overs occur at only one point in attφ and that the recognition sequences that direct the integration enzymes to their site of action are quite small, less than 2000 nucleotides each. Furthermore, no base pair homology was detected between attφ and its bacterial analog, attB. This result clearly demonstrates that λ integration can occur between chromosomes which have little, if any, homology. In this respect, λ integration is unique as a system of recombination since most forms of generalized recombination require extensive base pair homology.

An additional study on the genetic and physical distances in the left arm of the λ genome was described. Here, a large number of conditional lethal nonsense mutants were isolated and mapped, and a genetic map of the entire left arm, comprising a total of 18 genes, was constructed. Four of these genes were discovered in this study. A series of λdg transducing phages was mapped by heteroduplex electron microscopy and the relationship between physical and genetic distances in the left arm was determined. The results indicate that recombination frequency in the left arm is an accurate reflection of physical distances, and moreover, there do not appear to be any undiscovered genes in this segment of the genome.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Biology
Degree Grantor:California Institute of Technology
Division:Biology
Major Option:Biology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Edgar, Robert S.
Thesis Committee:
  • Unknown, Unknown
Defense Date:15 October 1969
Record Number:CaltechTHESIS:08112015-161712404
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:08112015-161712404
DOI:10.7907/V4T1-KJ37
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9098
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:20 Aug 2015 22:06
Last Modified:21 Dec 2019 04:46

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