[Lambda plasmidophages and their properties].

Plasmidphage lambda NM::pBR322 has been constructed in vitro and characterized. Under normal conditions the hybrid DNA molecule undergoes a lytic cycle of phage development, whereas in the presence of antibiotic lambda DNA replicates in the cell extrachromosomally as a plasmid. Properties of plasmidphage lambda NM::pBR322 have been compared with the earlier constructed lambda gt::pMB9. It has been demonstrated that plasmid pMB9 in vivo can be precisely excised from the lambda gt::pMB9.