The EXP1910IT line of corn (<i>Zea mays</i>) was developed through chemical mutagenesis to be resistant to the activity of imidazolinone herbicides. The novel variety was developed from ICI Seed’s inbred line UE95 and was selected for a mutation within the acetolactate synthase gene that resulted in this enzyme being insensitive to the activity of imazethapyr, the active ingredient of the herbicide Pursuit®. <br>Acetolactate synthase (ALS, also known as acetohydroxy acid synthase; AHAS) is involved in the conversion of threonine to alpha-aceto-alpha-hydroxybutyrate and pyruvate to alpha-acetolactate, which are key precursors in the biosynthesis of the essential branched-chain amino acids isoleucine and valine, respectively. Alpha-acetolactate is also a precursor in the synthesis of leucine.  Disruption of branched-chain amino acid synthesis by inhibition of ALS results in disrupted protein and DNA synthesis and ultimately plant death.  The modified corn line permits farmers to use imidazolinone herbicides for weed control in the cultivation of corn.<br>The imazethapyr tolerant trait in line EXP1910IT was selected following chemical mutagenesis by exposing pollen to ethyl-methane sulfonate. Mutagenized pollen was then used to fertilize the parent line, UE95, and progeny plants were screened for tolerance to imazethapyr. Ethyl-methane sulfonate is a commonly used chemical mutagen that affects DNA by chemically altering base pairs. The tolerance to imazethapyr resulted from a single nucleotide substitution within the ALS encoding gene. This substitution resulted in a single amino acid change (serine21 to asparagine21) in the sequence of the enzyme, which prevented the binding of imazethapyr to the active site, thus maintaining normal enzyme activity. Data from several generations of backcrossing demonstrated stable inheritance of the novel trait.<br>Based on the information provided, there are no novel proteins produced in line EXP1910IT. The single amino acid change within the active site of the ALS enzyme did not otherwise affect its activity except to provide tolerance to the herbicide Pursuit® at concentrations up to 500 uM. Other than tolerance to imidazolinone herbicides, the disease, pest and other agronomic characteristics of EXP1910IT were comparable to unmodified UE95 corn.