The lactose system inKlebsiella aerogenesV9A: 3. Specific repression of thelacoperon by melibiose and raffinose

Abstract

SUMMARYInKlebsiella aerogenesstrain V9A melibiose and raffinose fail to induce thelacoperon and strongly repress its induction by isopropyl-β-d-thiogalactopyranoside (IPTG). This repression is specific to thelacsystem and is not released by cAMP, which releases the catabolite repression exerted by glucose and sucrose. It is concluded that melibiose and raffinose bind to thelacrepressor molecule inKlebsiellaV9A, competitively displacing IPTG, and that the resulting complex is able to repress thelacoperon. OtherKlebsiellastrains tested show the same repression phenomenon.