2 types of auxotrophic mutants occurring by insertion of the ampicillin transposon into the chromosome of E. coli K-12]

Insertion of transpozone TnI determining ampicillin resistance into the E. coli K-12 chromosome resulted in formation of auxothrophic mutants of 2 types. The mutants of the first type carried thermosensitive mutation resulting in auxotrophy with respect to isoleucine at a temperature of 43 degrees C. Such mutants occurred with high frequency (up to 14 per cent with respect to the number of the survived cells with the chromosomes carrying inserted TnI) and had capacity for reversion to the phenotype of the wild type. The mutants of the second type occurred with a frequency 20--180 times lower than that of the mutants of the first type and did not reverse to the phenotype of the parent bacteria. It was found that the chromosome of E. coli K-12 possessed at least 7 sites available for transpozone TnI insertion.