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Phage Lambda’s Accessory Genes

Donald Court, Amos B. Oppenheim


Phage λ contains some 50 kbp of DNA, and approximately 50 genes have been revealed by analysis of mutants and phage proteins. Most of these genes are essential for perpetuation of the virus in either the lytic or the lysogenic mode of growth. For example, 27 genes are required for the phage to produce mature progeny and form plaques. Five other genes are required for repression, integration, and excision. Several other genes, which form the subject of this paper, are not absolutely required for either lysis or lysogeny. These genes are distributed in several places along the λ genome, and the regions carrying them can be deleted with minimal effects on phage development. Because they are not essential for “normal” phage development in standard hosts and under standard laboratory conditions these genes have been collectively designated as nonessential or dispensable. However, it is becoming clear that these genes are not functionless but, rather, they often have interesting and even essential roles in certain circumstances. Consequently, we prefer to call them accessory genes. In this paper, we review λ’s accessory genes and discuss their role with respect to both λ and Escherichia coli.

Since these genes are dispensable for “normal” λ development, they have not been studied extensively, and our understanding of their expression and function is limited. Nevertheless, we can make a few general statements about their roles. Some appear to be nonessential for phage growth because an analogous or compensating function exists in the host. Others are essential...

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