In vitro constructed plasmids containing both ends of bacteriophage Mu DNA express phage functions.

The construction of a plasmid carrying the right end PstI . B fragment of bacteriophage Mu DNA and of plasmids containing in addition the left end EcoRI.C fragment of Mu DNA into the vector pBR322 is described. Inversion of the G segment still occurs in all these plasmids. By marker rescue and complementation experiments the right PstI cleavage site was located to the left of gene Q. The composite plasmids inheriting also the left end EcoRI fragment of Mu DNA express both the immunity and killing functions of Mu and direct the in vitro synthesis of presumably Mu-specific polypeptides. These results demonstrates that Mu-specific functions can be analyzed from cloned fragments.