Mu: A transposable phage

Phage Mu is a phage that reproduces by transposition. A simplified cartoon of the Mu genetic map is shown below.

Note the following features of Mu phage:

The life cycle of phage Mu is shown in the cartoon below. (A) When Mu infects a sensitive host, the linear DNA enters the cell and the Mu DNA (i.e. not including the variable sequences of DNA acquired from the previous host) is inserted into the recipient genome via a non-replicative, "cut and paste" mechanism. (B) Lysogens of wild-type Mu are quite stable and are not induced by UV or other DNA damaging agents. However, derivatives of Mu with a temperature sensitive repressor -- Mu c(Ts) -- can be induced by shifting the lysogen to 42 C. (C) When the repressor is inactivated, the A and B proteins are expressed and Mu transposes by a replicative mechanism to 50 - 100 new sites on the chromosome. Meanwhile, late phage gene products are made (including phage heads, tails, lysis proteins, etc). The phage DNA is packaged by a headful mechanism, beginning by cutting the dsDNA in host sequences located about 100 bp from the left end of Mu. The length of Mu DNA is about 37 Kb and about 39 Kb are packaged into each head, so about approximately 2 Kb of host DNA is included on the right end of the packaged DNA. After assembly of the phage, the host is lysed, releasing 50-100 phage particles.

Mu derivatives (Mud) can be used to construct operon and gene fusions and for in vivo cloning.


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Last modified October 14, 2003