Lysogeny, Prophage Induction, and Lysogenic Conversion

Temperate phages can carry genes that affect the phenotype and behavior of their bacterial host. These genes can be considered extra genetic material in that they are not necessary for viral lytic growth or for the lysogenic lifestyle. This chapter describes circumstances under which foreign genes can be expressed. It first considers the life cycle of temperate phages. With this background, it then describes how foreign genes can be expressed in the lysogenic state. It then turns to a more detailed description of a particular temperate phage λ, with an emphasis on the regulatory mechanisms that are best understood for this phage. This description will facilitate an understanding of how foreign genes can be expressed during the process of prophage induction, and a particular example will be described. Importantly, for lysogenic conversion to occur, it is not necessary that the prophage remains functional as a virus that is capable of prophage induction or lytic growth. Foreign genes are most commonly expressed from a prophage in the lysogenic state. This pattern of expression is often termed lysogenic conversion, since it can change or convert the phenotype of the bacterial host. The chapter also reviews the gene organization of phage λ and then briefly describes the pattern of expression of these genes during lytic growth. RecA plays a central role in homologous recombination and DNA repair, catalyzing a complex set of DNA strand transfer reactions.