Vegetative recombination in bacteriophage Mu-1

Transduction of multi-copy plasmid pBR322 by bacteriophage Mu

The temperate bacteriophage Mu transduces the 4363 bp multi-copy plasmid pBR322 at frequencies similar to those of chromosomal markers. Plasmid transducing particles contain DNA molecules of Mu DNA length. Plasmid DNA is transduced as a head-to-tail oligomer that becomes circularized in the recipient cell. The rec system of the donor strain participates in oligomer formation and the rec system of the recipient strain is required for oligomer circularization. Possible mechanisms that may explain the origin of plasmid transducing particles are discussed.

Stability of plasmids R1-19 and R100 in hyper-recombinant Escherichia coli strains and in Salmonella typhimurium strains

Plasmids R1-19 and R100 dissociate in hyper-recominant Escherichia coli strains in a way that is similar to but slower than dissociation in Salmonella typhimurium. The results presented suggest that the molecular mechanism for plasmid dissociation in hyper-recombinant E. coli strains is different than that in S. typhimurium strains.

Chromosomal rearrangements by an IS2 insertion in phage Mu-1

We have isolated and characterized a mutant of temperate phage Mu-1 carrying an IS2 insertion in the middle of its beta region. This mutant gives rise spontaneously to secondary mutants which have deletions of different sizes adjacent to IS2. One particular derivative however, was found to have acquired an additional insertion sequence adjacent to IS2. This derivative gave rise to tertiary mutants carrying a deletion next to the tandem insertion. The tandem insertion was located at the same place in the Mu beta region as another 2.6 kb insertion independently isolated by Chow et al. (1977) and was found to be homologous to that insertion. The properties of this particular secondary mutant show that Mu phage particles lacking their S end are defective for growth and lysogenisation.

Transfection of Escherichia coli by Mu DNA

Infectivity of Mu DNA was demonstrated in Ca+ +-treated Escherichia coli cells that lacked the nucleases Exo V and Endo I. The efficiency of transfection is about 10(-7) per phage equivalent. Infectivity is destroyed by denaturation of Mu DNA, and cannot be restored by renaturation.

Model for the enchancement of lambde-gal integration into partially induced Mu-1 lysogens

Temperate phage Mu-1, which is able to integrate at random in its host chromosome, is also able to mediate integration of other circular deoxyribonucleic acid, as a lambda-gal mutant unable to integrate by itself. After mixed infection with lambda-gal and Mucplus, galplus transductants are recovered that have the lambda-gal integrated in any circular permutation, sandwiched between two complete Mu genomes in the same orientation, the whole Mu-lambda-gal-Mu structure being found at any location in the bacterial chromosome. Here we show that such a lambda-gal can integrate in an induced Mu lysogen. In this case the lambda-gal is again in any circular permutation, between two Mu in the same orientation, but it is always located at the site of the original Mu prophage, and the two surrounding Mu have always the same genotype as the original Mu prophage. Active Mu replication functions are not essential for that process to occur. This suggests that bacterial replication may generate two Mu copies that in some way can regenerate a Mu attachment site that recombines with the lambda-gal. A model is presented that accounts for these observations, may be helpful for understanding some complex features of Mu development, and may possibly offer a basis for explaining spontaneous duplications.