| Abstract: | The hybrid plasmid RP4::D3112 becomes unstable in Escherichia coli K-12 cells under certain growth conditions. The deletion mutants of this plasmid are formed at a high frequency. All the deletions selected have a specific feature: they start in the left end, at the point of joining of plasmid and phage DNA, and remove different portions of the phage genome. The deletion mutants have been used for genetic mapping of D3112. We have localized the repressor gene cI (0-1.3 kb), 3 early genes (1.3-14.2 kb) and two groups of late genes (14.2-29.9 and 29.9-38 kb). Electron microscope studies of RP4::D3112 DNA and its deletion derivatives have shown that integration of D3112 genome in RP4 occurs through the ends of the genome, without permutations. It appears that bacterial nucleotide sequences joined to DNA from mature D3112 particles, to the right end of D3112 genome, are lost. Thus, transposable phages D3112 of Pseudomonas aeruginosa and E. coli Mu phage have some similarities in the genome organization and in the way of their integration into the host DNA. |
