[Mutation in the glmS gene responsible for the cell wall synthesis increases resistance to the herbicide amitrole in the cyanobacterium Synechocystis sp. PCC6803].

A DNA fragment transforming the cells of the cyanobacterium Synechocystis sp. PCC 6803 to amitrole (3-amino-1,2,4-triazole) resistance was cloned from the Atr2 mutant resistant to this herbicide. The transforming activity of the cloned fragment was shown to be related to the missence-mutation "Val250-->Leu250" in the glmS gene encoding glucosamine-6-phosphate synthase, a key enzyme of cell wall synthesis. The amino acid substitution is localized in the central nonconservative part of the GlmS protein, far from two reaction centers positioned at the ends of a polypeptide. It is suggested that the mutant protein has lost sensitivity to amitrole. In the wild type strain, this herbicide causes conditional glucosamine auxotrophy (exogenous glucosamine restores ability of the cells to row in the presence of the lethal amitrole concentrations). Val250 is proposed to be allosteric binding site of AM in the GlmS protein of cyanobacterium.