[Localization of the tetracycline resistance determinant in Streptomyces coelicolor A3(2)].

It was shown that the rate of segregation of variants sensitive to tetracycline by Str. coelicolor A3(2) was high, i. e. 0.1 per cent. The tetracycline sensitive variants in their turn had an ability to reverse tetracycline resistance at a rate of 10(-2)--10(-4). Such a genetically unstable determinant of tetracycline resistance is localized on the chromosome between markers ade C (V10) and arg A1. The data are indicative of the fact that formation of tetracyctine sensitive variants could not be associated with elimation of the plasmid carrying the tetracycline resistant determinant or deletion. Formation of such variants as a result of point mutations is also hardly probable. It is suggested that the genetic instability of tetracycline resistance is due to recombination events (transposition of the controlling element) involving and expelling expression of the tetracycline resistance gene(s).