An  operon  is a group of functionally related genes under the control
   by  a  single  on-off  "switch"  called  an  operator which is usually
   located within the promoter.
   The  E. coli trp operon contains 5 genes in the pathway for tryptophan
   (an amino acid) synthesis.
   A  separate  regulatory  gene  codes  for a repressor that is normally
   inactive.
<BR><LI> operon on
<BR><LI> operon off
<P>
   Review:  <A ClAsS=MID Href="../../../med/Vid/Discover2e/ch16a04_trp-repressor.dcr" oNClick="popurlt('../../../../med/Vid/Discover2e/ch16a04_trp-repressor.dcr');txtcolor('trp_operon3','gray');return false;" Id=trp_operon3><iMg sRc="/images/shockwave.gif" aLt='' boRDer=0></A>