Plasmid vectors derived from phage Mu allow direct selection of transformants containing cloned HindIII and PstI fragments.

The vector plasmids pKN001 and pKN80 both contain the EcoRi.C fragment of E.coli phage Mu DNA which codes for a killing function that is efficiently expressed upon transformation into Mu-sensitive bacteria. By in vitro insertion of HindIII fragments at the single HindIII site of pKN80 or of PstI fragments at the single PstI site of pKN001 the killing function is inactivated. The resulting plasmids have a selective advantage over the religated vector when transformed into Mu-sensitive bacteria. More than 90% of the transformations contain hybrid plasmids. These results show the usefulness of Mu DNA containing plasmids pKN001 and pKN80 as vectors that allow the direct selection for recombinant plasmids.