[Repair of recombinant plasmids].

Comparative analysis of UV-sensitivity was carried out on plasmids of various molecular weight. Recombinant plasmids containing fragments of prokaryotic DNA (E. coli, phage lambda) are repaired in E. coli cells more effectively than those containing eukaryotic DNA fragments. It was also shown that UV-sensitivity of recombinant plasmids is independent of their molecular weight provided that the active repair process in fact occurs. UV-sensitivity was strongly proporational to DNA size only when E. coli double mutant strain was used as host. The survival of plasmids strongly increased after M. luteus UV-endonuclease treatment when E. coli mutant strain uvr- was used as host, but remained practically constant in case of wild type strain. Agarose gel electrophoresis data provide evidence that DNA double-stranded breaks appear un UV-irradiated as well as in UV-endonuclease treated plasmids. One can suggest that UV-inactivation of plasmids results from DNA breaking as a consequence of repair gaps overlap when wild type strain is used as host. Mathematical analysis was carried out assuming this possibility. Experimental data are shown to fit theoretical values calculated assuming that the repair gap size in one DNA strand is equal to 2000-3000 bases.