Genetic analysis of the cloned genome of phage Mu

Randomly sheared fragments of Mu cts62 DNA have been cloned into the EcoRI cleavage site of plasmid p0P203(UV-5)-3, a derivative of pMB9 containing the lactose operator promoter, using poly (dA · dT) tailing with terminal transferase. The extent of Mu DNA carried by the recombinant plasmids was determined genetically by crosses with known markers in essential genes of Mu in rec⁺ backgrounds. Plasmids which rescued essential genes were transformed to rec^? backgrounds to check for expression of the Mu genes. Plasmids were found which rescued and complemented 23 of the 24 essential genes of Mu. Many of these plasmids carried overlapping segments of the Mu genome. The plasmid library was also screened for clones containing the nonessential genes gin and mom. Clones carrying gene A were not found in the initial screening, however, several clones which were resistant to infection by Mu due to expression of the Mu repressor were able to rescue and complement a D108cts-MuAts hybrid phage at 43°.