Deletions of plasmid pRP3.1ts12 derived from RP1 leading to the suppression of the thermosensitive ts12 mutation and mucoid phenotype induction in Escherichia coli K-12

Properties of a temperature-sensitive in replication mutant pRP3.1ts12 derived from the broad host range RP1 plasmid have been studied. pRP3.1ts12 is a shortened variant of the temperature-sensitive RP1ts12 mutant carrying a deletion in a region from 2.3 to 7.6 MD. In contrast to RP1ts12, the plasmid pRP3.1ts12 is a leaky ts mutant and is characterized by an elevated frequency of reversions to the temperature-independent phenotype. Temperature-independent derivatives of pRP3.1ts12 were studied. Approx. 15% of these were found to induce mucoid growth of the host cells. As revealed from restriction endonuclease analysis, most of the latter derivatives contain deletions of small DNA segments in the region 0.56 to 2.3 MD of the RP1 map. The possible nature of the gene(s), whose deletions suppress the temperature-sensitive ts12 mutation and results in superproduction of Escherichia coli capsular poly-saccharide is discussed.