Studies on polylysogens containing λN^-cl^- prophages II. Role of high multiplicities in lysogen formation by λN^-cl^- phage

Abstract

Results of the experiments presented in this paper show that λN^-cI^- phage can lysogenize a nonpermissive host Escherichia coli when it infects at very high multiplicities (around 100), and λN^-cI^-cII^- and λcIII^-N^-cI^- lysogenize poorly at similar high multiplicities. The latter two phages lysogenize with appreciable frequency when either λN^-cI^- or λint-cN^-cI^-cII^- is used as helper. The phages, λN^-cI^-, λN^-cI^-cII^-, and λcIII^-N^-cI^- can lysogenize also at relatively low m.o.i. of 20 in presence of the above λint-c helper, and the λint-cN^-cI^-cII^- phage alone forms converted lysogens at an m.o.i. as low as 12. All these results suggest that the establishment of prophage integration by λN^-cI^- is positively regulated, like λN⁺cI⁺ phage, by the cII/cIII-promoted expression of the int gene of λ, and under the N^- condition, high multiplicities are needed to provide optimum levels of cII and cIII products, especially the latter.