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Bacteriophage P22 Antirepressor and Its Control

Miriam M. Susskind, Philip Youderian


In the past 10 years, it has become increasingly clear that the genome of temperate Salmonella phage P22 is organized and regulated in much the same way as the genome of λ (or of other related lambdoid coliphages). Alignment of the P22 and λ prophage genetic maps (Fig. 1) reveals that the two genomes are, for the most part, composed of analogous clusters of functionally related genes arranged in the same order. This congruence of genetic structure and function is particularly striking in the left half of the prophage, where there is a one-to-one correspondence between many individual P22 and λ genes, including the genes encoding major regulatory proteins as well as their sites of action. Thus, the regulatory mechanisms responsible for temporal control of gene expression during lytic development and for establishment and maintenance of repression in P22 closely parallel the mechanisms that operate in λ.

P22 and λ not only share common features of genetic and physiological organization but also show a considerable degree of DNA sequence homology (Skalka and Hanson 1972). Furthermore, P22 and λ recombine in vivo to produce viable hybrids (Gemski et al. 1972; Botstein and Herskowitz 1974). For all of these reasons, P22 has properly come to be considered a member of the lambdoid family. However, P22 differs profoundly from λ (and other lambdoid coliphages) in many properties, most of which are determined by genes in the right half of the prophage map. The pathway of P22 capsid assembly differs substantially from the λ...

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