Cognate Putative Nuclear Localization Signal Effects Strong Nuclear Localization of a GFP Reporter and Facilitates Gene Expression Studies in Caenorhabditis Elegans

Targeting a gene expression reporter, usually the green fluorescent protein (GFP), to the nucleus via a translationally fused nuclear localization signal (NLS) greatly facilitates recognition and identification of the reporter-expressing cells in Caenorhabditis elegans. Presently circulating nematode transcriptional gene expression vectors use the viral NLS from simian virus 40 (SV40) large T antigen. This NLS, however fails to ensure sufficient localization of the GFP peptide to the nucleus. We modified the common transcriptional reporter SV40 NLS-GFP by adding to its C terminus a cognate putative NLS from the transcription factor egl-13. The EGL-13 NLS effected clear contrast in fluorescence intensity between the nucleus and the cytoplasm in cells with strong reporter signal and efficiently highlighted the nucleus in tissues with weak reporter expression in a wide range of tested tissues. The SV40 NLS-GFP-EGL-13 NLS vector should become a valuable tool for gene expression studies in C. elegans.