| Abstract: | Hershey circles and linear tandem aggregated forms of DNA have been obtained in vitro and treated with polynucleotide ligase to form phosphodiester bond. Using zone centrifugation in glycerol gradient covalently closed circles and linear dimers have been purified and their biological activity investigated. It was found that closed circular molecules lost most, if not all, of their activity in CaCl2-dependent system. In order to investigate the biological activity of tandem dimer molecules, hybrid dimers consisting of DNA's from lambda C1857 and lambda 1434 have been obtained. In plaque assay with the appropriate non-permissive strains of E. coli the efficiency of infectivity of hybrid dimers was measured. Biological activity of dimer molecules sealed with ligase was about 5% of the activity of linear monomers. Ig has been suggested that tandem dimers of lambda DNA joined by phosphodiester bond are able to penetrate into the CaCl2-treated host cells and both components of dimers are active during subsequent multiplication. |
