The loss of a large DNA fragment is associated with an aerial mycelium negative (Amy-) phenotype of Streptomyces cattleya.

Hybridization of various Streptomyces cattleya aerial mycelium negative (Amy-) mutants with a probe containing the gene for argininosuccinate synthetase (pTG17) has revealed the presence of two different types of mutants (stable and unstable). Stable mutants appear to have lost all or part of the region covered by the probe, while the unstable mutants demonstrate no detectable changes in this region. In one group of stable mutants (those demonstrating a partial loss of sequences hybridizing to the probe), a 4.17 kb extrachromosomal element was detected, which hybridized with the pTG17 probe. The significance of this finding is discussed with reference to the genetic instability of the genus Streptomyces.