Identification of a protein coded by pR plasmid and involved in SOS repair in E. coli

The TP120 plasmid is known to determine enhanced UV survival in E. coli wild type an uvrB and PolA mutants but not in RecA mutant. In order to analyze the function involved in the SOS repair, we have constructed a new plasmid named pR derived by cleavage of TP120 with Hind III endonuclease. This new plasmid maintains the Ap and UV resistance. The insertion of Tn5 transposon in the plasmid allows to select several pR::Tn5 plasmids whose UV resistance was inactivated by the transposition. The comparison of the protein synthesis in the minicells of the pR and pR::Tn5 shows that the pR codes for a 22.000 M.W. dalton protein which is absent in protein pattern of pR::Tn5.