Editing Lambda phage (section)

==Lytic vs. lysogenic==
[[File:Lambda temperate life cycle.png|thumbnail|Diagram of temperate phage life cycle, showing both lytic and lysogenic cycles.]]
An important distinction here is that between the two decisions; lysogeny and lysis on infection, and continuing lysogeny or lysis from a prophage. The latter is determined solely by the activation of RecA in the SOS response of the cell, as detailed in the section on induction. The former will also be affected by this; a cell undergoing an SOS response will always be lysed, as no cI protein will be allowed to build up. However, the initial lytic/lysogenic decision on infection is also dependent on the cII and cIII proteins.

In cells with sufficient nutrients, protease activity is high, which breaks down cII. This leads to the lytic lifestyle. In cells with limited nutrients, protease activity is low, making cII stable. This leads to the lysogenic lifestyle. cIII appears to stabilize cII, both directly and by acting as a competitive inhibitor to the relevant proteases. This means that a cell "in trouble", i.e. lacking in nutrients and in a more dormant state, is more likely to lysogenise. This would be selected for because the phage can now lie dormant in the bacterium until it falls on better times, and so the phage can create more copies of itself with the additional resources available and with the more likely proximity of further infectable cells.

A full biophysical model for lambda's lysis-lysogeny decision remains to be developed. Computer modeling and simulation suggest that random processes during infection drive the selection of lysis or lysogeny within individual cells.<ref>{{cite journal | vauthors = Arkin A, Ross J, McAdams HH | title = Stochastic kinetic analysis of developmental pathway bifurcation in phage lambda-infected Escherichia coli cells | journal = Genetics | volume = 149 | issue = 4 | pages = 1633–1648 | date = August 1998 | pmid = 9691025 | pmc = 1460268 | doi = 10.1093/genetics/149.4.1633 }}</ref>  However, recent experiments suggest that physical differences among cells, that exist prior to infection, predetermine whether a cell will lyse or become a lysogen.<ref>{{cite journal | vauthors = St-Pierre F, Endy D | title = Determination of cell fate selection during phage lambda infection | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 105 | issue = 52 | pages = 20705–20710 | date = December 2008 | pmid = 19098103 | pmc = 2605630 | doi = 10.1073/pnas.0808831105 | doi-access = free | bibcode = 2008PNAS..10520705S }}</ref>