The invention provides methods of determining the presence of a nuclear localization
signal and / or the presence of a nuclear export
signal in a
protein of interest. The invention further provides chimeric nucleic acids and recombinant host cells for use in such methods. Additionally provided is a
nucleic acid molecule encoding a modified LexA
protein, wherein the modified LexA
protein has no nuclear localization
signal, as well as the modified LexA protein itself. In the nuclear import
assay, if a protein of interest fused to a mLexA-Gal4AD
hybrid contains a functional NLS, the fusion product will enter the
yeast cell nucleus and activate the expression of reporter genes. In the nuclear export
assay, if a protein of interest fused to a mLexA-SV40 NLS-Gal4AD
hybrid contains a functional NES, the fusion product localized to the
cell nucleus will exit into the
cytoplasm, decreasing the
reporter gene expression levels.