To test the hypothesis that Hmp overexpression , and not that of other NsrR-regulated gene products ( such as ytfE , hcp -- hcr , tehA , tehB and ygbA ) is responsible for hypersensitivity to peroxynitrite , we determined the effect of peroxynitrite on a double mutant ( hmp and nsrR ) .
To determine the contribution of other NsrR-regulated genes to nitrosative-stress resistance , we constructed insertion mutations in hcp , ygbA , ytfE , STM1808 and yeaR ( Experimental Procedures ) .