[Phasmids. Properties and the use in genetic engineering. II. Packing in vitro. Lysogeny of Escherichia coli K-12]

Circular monomeric lambda DNA molecules were used as a substrate for packaging reaction in vitro. For obtaining lambda DNA in circular monomeric form only, Escherichia coli recA plasmid bearing cells were used. This hybrid DNA molecule which we designated phasmid lambda pMYF11, is the pBR322 plasmid in which lambda 47.1 DNA was introduced in vitro. The phasmid can exist in the plasmid form or as a non-defective phage. The efficiency of packaging reaction in vitro proved to be similar for monomeric circular and linear form of phasmid DNA molecules. The cI- variant of the phasmid is not able to exist as a plasmid even in the cells containing homoimmune prophage. Still, cI+ phasmid variants capable of lysogenizing arise with low frequency, as a result of recombination between the resident cI+ prophage and infecting cI- phasmid.