The ilv-leu operon of bacillus subtilis comprises seven genes necessary for the biosynthesis of isoleucine, valine, and leucine. the structural genes of this operon are transcribed when these amino acids are deficient in the cell. the vana operon codes enzymes that modify the binding targets of antibiotic vancomycin and therefore give antibiotic resistance to the bacteria. the structural genes of this operon are transcribed when the antibiotic vancomycin is present in the environment. and the vana operon is operon.