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Developmental switches in a family of temperate phages
Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

P2 is the prototype phage of the non-lambdoid P2 family of temperate phages. A developmental switch determines whether a temperate phage will grow lytically or form lysogeny after infection. P2 related phages have two face-to-face located promoters controlling the lysogenic and the lytic operon respectively, and two repressors. The immunity C repressor of P2 is the first gene of the lysogenic operon and it represses the lytic promoter. The Cox protein, the first gene of the lytic operon, is multifunctional. It represses the lysogenic promoter, acts as a directionality factor in site-specific recombination and activates the PLL promoter of satellite phage P4.

This thesis focuses on comparisons between the developmental switches of P2 and the two heteroimmune family members, P2 Hy dis and WΦ. A characterization of the developmental switch region of P2 Hy dis identifies a directly repeated sequence which is important for C repression. P2 Hy dis Cox can substitute for P2 Cox in repression of the P2 lysogenic promoter, excision of a P2 prophage and activation of P4 PLL. The P4 ε protein can derepress the developmental switch of P2 Hy dis.

Functional characterizations of the C repressors and Cox proteins of P2 and WΦ show that both C repressors induce bending of their respective DNA targets. WΦ C, like P2 C, has a strong dimerization activity in vivo, but there are no indications of higher oligomeric forms. Despite the high degree of identity in the C-terminus, required for dimerization in P2 C, they seem to be unable to form heterodimers. The two Cox proteins are predicted to have identical secondary structures containing a helix-turn-helix motif believed to be involved in DNA binding. It is, however, not possible to change the DNA specificity of P2 Cox to that of WΦ Cox by swapping the presumed recognition helix. P2 Cox recognizes a sequence repeated at least six times in the different targets, while WΦ Cox seems to recognize a single direct repeat. In contrast to P2 Cox, WΦ Cox binds with a stronger affinity to the switch region than to the attachment site (attP). The Cox proteins induce a strong bend in their DNA targets, strengthening the hypothesis that they have a structural role at site-specific recombination. Both proteins show a capacity to oligomerize, but P2 Cox has a higher tendency to form oligomers than WΦ Cox.

The P2 integrase mediates site-specific recombination leading to integration or excision of the P2 genome in or out of the host chromosome. P2 Cox controls the direction by inhibiting integration and promoting excision. In this work it is shown that Cox and Int bind cooperatively to attP.

Place, publisher, year, edition, pages
Stockholm: Institutionen för genetik, mikrobiologi och toxikologi , 2005. , 77 p.
National Category
Genetics
Identifiers
URN: urn:nbn:se:su:diva-644ISBN: 91-7155-104-2 (print)OAI: oai:DiVA.org:su-644DiVA: diva2:196490
Public defence
2005-09-29, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2005-09-06 Created: 2005-09-06 Last updated: 2010-05-05Bibliographically approved
List of papers
1. Characterization of the developmental switch region of bacteriophage P2 Hy dis
Open this publication in new window or tab >>Characterization of the developmental switch region of bacteriophage P2 Hy dis
2001 In: Virology, ISSN 0042-6822, Vol. 290, no 2, 199-210 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24026 (URN)
Note
Part of urn:nbn:se:su:diva-644Available from: 2005-09-06 Created: 2005-09-06Bibliographically approved
2. The oligomeric states of the two immunity repressor proteins of the heteroimmune coliphages P2 and WΦ, and their effects on DNA topology
Open this publication in new window or tab >>The oligomeric states of the two immunity repressor proteins of the heteroimmune coliphages P2 and WΦ, and their effects on DNA topology
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-24027 (URN)
Note
Part of urn:nbn:se:su:diva-644Available from: 2005-09-06 Created: 2005-09-06 Last updated: 2010-01-13Bibliographically approved
3. A comparative analysis of the multifunctional Cox proteins of the two heteroimmune phages P2 and WΦ
Open this publication in new window or tab >>A comparative analysis of the multifunctional Cox proteins of the two heteroimmune phages P2 and WΦ
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-24028 (URN)
Note
Part of urn:nbn:se:su:diva-644Available from: 2005-09-06 Created: 2005-09-06 Last updated: 2010-01-13Bibliographically approved
4. Cooperative interactions between bacteriophage P2 integrase and its accessory factors IHF and Cox
Open this publication in new window or tab >>Cooperative interactions between bacteriophage P2 integrase and its accessory factors IHF and Cox
2005 (English)In: Virology, ISSN 0042-6822, E-ISSN 1096-0341, Vol. 332, no 1, 284-294 p.Article in journal (Refereed) Published
Abstract [en]

Bacteriophage P2 integrase (Int) mediates site-specific recombination leading to integration or excision of the phage genome in or out of the bacterial chromosome. Int belongs to the large family of tyrosine recombinases that have two different DNA recognition motifs binding to the arm and core sites, respectively, which are located within the phage attachment sites (attP). In addition to the P2 integrase, the accessory proteins Escherichia coli IHF and P2 Cox are needed for recombination. IHF is a structural protein needed for integration and excision by bending the DNA. As opposed to lambda, only one IHF site is found in P2 attP. P2 Cox controls the direction of recombination by inhibiting integration but being required for excision. In this work, the effects of accessory proteins on the capacity of Int to bind to its DNA recognition sequences are analyzed using electromobility shifts. P2 Int binds with low affinity to the arm site, and this binding is greatly enhanced by IHF. The arm binding domain of Int is located at the N-terminus. P2 Int binds with high affinity to the core site, and this binding is also enhanced by IHF. The fact that the cooperative binding of Int and IHF is strongly reduced by lengthening the distance between the IHF and core binding sites indicates that the distance between these sites may be important for cooperative binding. The Int and Cox proteins also bind cooperatively to attP.

Keyword
Bacteriophage, Site-specific recombination, Integrase, IHF, Cox, Directionality factor
Identifiers
urn:nbn:se:su:diva-23610 (URN)10.1016/j.virol.2004.11.015 (DOI)
Available from: 2005-02-24 Created: 2005-02-24 Last updated: 2010-05-12Bibliographically approved

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