The product of the lmaA gene was demonstrated
to encode a 20-kDa protein capable of inducing a
specific delayed hypersensitivity reaction in L. monocytogenes-immune
mice (19). Cell fractionation studies and
immunoblotting experiments have located the ImaA gene
product in the cell wall fraction. Furthermore, the lmaA
sequence was found to be uniquely present in L. monocytogenes
isolates. Subsequent nucleotide sequence analysis has
demonstrated that the ImaA gene is part of an operon and is
preceded by the ImaB gene, which encodes a 14-kDa polypeptide.
The role of the ImaBA operon remains to be
determined