Bacteriophage λ: The Lysogenic Pathway

Abstract

Coliphage λ is a temperate phage, so-called because it can grow in two distinct ways. During lytic growth, common to both temperate and intemperate phage, the virus chromosome is usually replicated several hundredfold within the span of a single cellular generation, the replicas are packaged into mature virus particles by newly synthesized virus proteins, and the particles are released as a result of cell lysis. Temperate viruses alone, however, are capable of growing in harmony with their hosts. Lambda, the best studied of the temperate coliphages, accomplishes this by synthesizing a protein that promotes the insertion of the virus chromosome into the host chromosome and by synthesizing a repressor that inhibits the further expression of virus genes. The resulting cell is called a lysogen, the process, lysogenization, and the inserted virus chromosome, prophage. [See Herskowitz (1973) for a recent review.]