Involvement of two genes of superinfecting phage Kappa in curing and induction of prophage Psi in Serratia marcescens HY

Prophage Ψ carried along with prophage y by Serratia marcescens HY is subject of moderate curing at heteroimmune superinfection of cells from stationary phase with phage χ. Curing becomes considerably more frequent when the bacteria are non‐iysogenic for y. Both Ψ, y ‐double‐lysogenic and Ψ‐single‐lysogenic cells with a mutation in the ink gene are very efficiently cured of Ψ if infected by χ tay , although this mutant was characterized as being deficient in transactivation of certain genes in prophage y. On the other hand to get efficiently cured after χ wild‐type infection these cells too must be devoid of a y prophage. Thus a y function turned on by tay + seems to counteract the elimination of Ψ. However, interestingly enough Ψ curing is boosted by a further y function under special circumstances. Efficient curing depends on an intact χ tap gene, a gene reported to cause transactivation of certain Ψ genes. Curing at χ tay infection is specifically accompanied by induction of the Ψ prophage in a part of the infected cells. However, there is no such induction at χ wild‐type infection, either in the absence or presence of a y prophage. An explanation of these findings is suggested which includes an antirepressive effect exerted on Ψ and a hypothetical interaction between the products of genes tap and tay .