The effect of Q expression on commitment to lysogeny in phage lambda.
Sine Lo Svenningsen, Dept. of Biology, University of Copenhagen

The regulatory circuit controlling the lysis-lysogeny decision of bacteriophage lambda is a paradigm for developmental genetic networks. In the lambda system the decision is made based on the expression trajectory of the CII protein. The organization of the lambda regulatory network is such that it is impossible to proceed down one developmental pathway without going at least part way down the other as well, but eventually the cell becomes committed to the chosen developmental strategy. The commitment to lysogeny is manifested by repression of the pR and pL promoters by CI, and the commitment to lytic development occurs by execution of the late gene expression cascade by the antitermination protein Q. I will discuss our recent experiments on the role of the Q protein in the commitment process. We find that ectopic expression of Q early after infection overrules the lysogenic decision, whereas it has no effect on a stable, committed lysogen. We hypothesize that a key factor in determining the time of commitment is the number of lambda chromosomes contained in the cell.

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