Ph.D Thesis

Ph.D StudentVerkin Ekaterina
SubjectPolarity and Temporal Regulation in Bacteriophage Lambda
DepartmentDepartment of Biology
Supervisor ASSISTANT PROFESSOR Jonathan Kuhn
Full Thesis textFull thesis text - English Version


    The Q protein of bacteriophage lambda mediates antitermination in the pR′ operon and is required for the expression of the late genes that are responsible for the phage capsid and tail, DNA packaging and cell lysis. Termination at the tR′ terminator is eliminated in the presence of Q. There are conflicting reports about the action of the Q protein downstream: some investigations show that Q can override terminators while others show that nonsense mutations can lead to polarity, albeit “localized”. This polarity seems to differ from the classical type because just one or several adjacent genes are affected, but not those further downstream. In the present investigation, it was shown that besides the pR′ promoter there are no other promoters within the pR′ operon and all the late genes are transcribed as a single polycistronic mRNA which doesn’t undergo post-transcriptional processing. An amber mutation at the start of the D gene leads to classical genetic polarity. All late genes that were examined and lie downstream of the Damber mutation are affected similarly and to the same extent. Initially the mutation causes little polarity, but polarity becomes pronounced at later times in the life cycle. Nonsense suppressors, mutation of the rho gene and over-expression of the Q protein relieve this polarity. In addition, “localized polarity” is not associated with differential stability of RNA corresponding to different late genes. At the same time, the results of the present work show that the morphogenetic genes seem to be organized in temporal modules. The time of expression within such a module is essential for the formation of viable progeny.

  From the results on polarity and the study of temporal regulation, it seems apparent that phenomenon of “localized polarity” most likely reflects subunit interactions in multi-protein complexes. Both the time of appearance and the relative amounts of the proteins during morphogenesis seem to be critical. That is, "localized polarity" takes place at the level of assembly of the virion.