Quantitative kinetic analysis of the bacteriophage λ genetic network

Oren Kobiler, Assaf Rokney, Nir Friedman, Donald L. Court, Joel Stavans, Amos B. Oppenheim*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

92 Scopus citations


The lysis-lysogeny decision of bacteriophage λ has been a paradigm for a developmental genetic network, which is composed of interlocked positive and negative feedback loops. This genetic network is capable of responding to environmental signals and to the number of infecting phages. An interplay between CI and Cro functions suggested a bistable switch model for the lysis-lysogeny decision. Here, we present a real-time picture of the execution of lytic and lysogenic pathways with unprecedented temporal resolution. We monitor, in vivo, both the level and function of the CII and Q gene regulators. These activators are cotranscribed yet control opposite developmental pathways. Conditions that favor the lysogenic response show severe delay and down-regulation of Q activity, in both CII-dependent and CII-independent ways. Whereas CII activity correlates with its protein level, Q shows a pronounced threshold before its function is observed. Our quantitative analyses suggest that by regulating CII and CIII, Cro plays a key role in the ability of the λ genetic network to sense the difference between one and more than one phage particles infecting a cell. Thus, our results provide an improved framework to explain the longstanding puzzle of the decision process.

Original languageAmerican English
Pages (from-to)4470-4475
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number12
StatePublished - 22 Mar 2005
Externally publishedYes


  • Gene regulation
  • Green fluorescent protein
  • Lysis
  • Lysogeny


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