Using the methods of molecular cloning permitted to show that riboflavin operon of Bacillus subtilis contains four promoters. Three of them are functionally active in the Bacillus subtilis system. The main promoter of the operon with regulatory region was cloned in plasmid pPL603. Cells containing the constructed plasmid pGM32 are resistant to chloramphenicol. The level of resistance is regulated by concentration of riboflavin (the effector of operon). The following model of rib-operon has been proposed: (Formula: see text).