The regulatory genes lanI and lndI have been cloned from the landomycin A (LaA) producer Streptomyces cyanogenus S136 and from the landomycin E (LaE) producer Streptomyces globisporus 1912, respectively and both have been sequenced. A culture of S. globisporus I2-1 carrying a disrupted lndI gene did not produce LaE and other related intermediates. Complementation of S. globisporus I2-1 with either the lndI or lanI gene reconstituted LaE production indicating that LanI and LndI are involved in activation of structural genes in the respective clusters. Structural features of these regulatory genes are discussed.