An A to T base change was introduced into exon 8 which caused the substitution of tyrosine, residue 385, with phenylalanine (Y385F). Numbering is based on numbering for the sheep protein. The actual mouse modification is Y371F. A floxed neomycin resistance cassette was introduced in intron 9. The cyclooxygenase function was inactivated but not the peroxidase function. (J:109548)