Green fluorescent protein (GFP) is widely used as a reporter in determining gene expression and protein localization. The present invention provides fusion proteins with a half life of ten hours or less with several embodiments having half lives of 4 hours or less. Such proteins may be constructed by fusing C-terminal amino acids of the degradation domain of mouse ornithine decarboxylase (MODC), which contains a PEST sequence, to the C-terminal end of an enhanced variant of GFP (EGFP). Fluorescence intensity of the fusion protein in transfected cells is similar to that of EGFP, but the fusion protein, unlike EGFP, is unstable in the presence of cycloheximide. Specific mutations in the MODC region have resulted in mutants with varying half lives, useful for a variety of purposes.