Evidence for different binding sites on the 33‐kDa protein for DCMU, atrazine and QB

Two DCMU‐resistant strains of the cyanobacterium Synechocystis 6714 were used to analyse the binding sites of DCMU, atrazine and Q B . DCMU r ‐II A was DCMU and atrazine resistant; it presented an impaired electron flow and its 33‐kDa protein was weakly attached to the membrane. DCMU r ‐II B , derived from the former, simultaneously regained atrazine sensitivity, normal electron flow and a tight linkage of the 33‐kDa protein to the membrane. This mutant shows that loss of DCMU binding does not necessarily affect the binding of either atrazine or Q B . The role of the 33‐kDa protein is discussed.