[Localization of the genes coding for the specific modification-restriction system in the E. coli tF strain]

The recombinant Escherichia coli tF strain has been shown to have its own specific modificational and restrictional system. In order to establish the location of genes, coding this system a plasmid has been isolated from the investigated strain, which substantiates the resistance to streptomycin. The plasmid DNA has been transformed into a recipient strain, E. coli O, which has no modificational and restrictional system of its own. The newly obtained E. coli O (ptF) transformants also have proved negative with regard to their testing for the presence of a specific modificational and restrictional system. The conclusion follows that the genes, coding the modificational and restrictional system of the E. coli tF strain are not located in the plasmid isolated from it.