Prophage y carried along with prophage y by Serrutiu marcescens HY is subject of moderate curing at heteroimmune superinfection of cells from stationary phase with phage x. Curing becomes considerably more frequent when the bacteria are non-lysogenic for y.
Both y,y-double-lysogenic and y-single-lysogenic cells with a mutation in the ink gene are very efficiently cured of y if infected by xtuy, 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 x wild-type infection these cells too must be devoid of a y prophage. Thus a y function turned on by tuy' seems to counteract the elimination of tp. However, interestingly enough y curing is boosted by a further y function under special circumstances. Efficient curing depends on an intact xtup gene, a gene reported to cause transactivation of certain y genes.
Curing at xtay infection is specifically accompanied by induction of the y prophage in a part of the infected cells. However, there is no such induction at x 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 y and a hypothetical interaction between the products of genes tap and tuy.
Two heteroimmune prophages, y~ and y , which are integral parts of strain HY of Serratia marcescens, appear to be subject to a so-called transactivation by superinfecting phage x. These activities were assigned to x genes termed tap and ray, respectively. The process ') If not otherwise stated phage were grown on HY(yi,y )-ink-34. ' ) Prophages are given in the text in the chronological order of lysogenization.
' in y curing is given at the end of this section.