Mutation in the glmS gene controlling cell wall synthesis increases resistance to the herbicide amitrole in cyanobacterium Synechocystis sp PCC6803

A DNA fragment transforming cells of the cyanobacterium Synechocystis sp. P CC6803 to amitrole (3-amino-1,2,4-triazole) resistance was cloned from cell s of the Atr2 mutant resistant to this herbicide. The transforming activity of the cloned fragment was shown to be associated with the missense mutati on "Val250 --> Leu250" in the glmS gene-encoding glucosamine-6-phosphate sy nthase, the key enzyme of cell wall synthesis. The amino acid substitution is located in the central, nonconservative region of the GlmS protein, far from the two reaction centers positioned at the polypeptide ends. It is sug gested that the mutant protein has lost sensitivity to amitrole. In the wil d-type strain, this herbicide causes conditional glucosamine auxotrophy (ex ogenous glucosamine restores cell ability to grow in the presence of lethal amitrole concentrations). It is proposed that Val250 is an allosteric bind ing site of the herbicide in the GlmS protein of the cyanobacterium.