Green Fluorescen t Protein as a Quantitativ e Reporter of Relativ e Promoter Activity in E. col i

Green fluorescent protein (GFP) has b e come a valuable tool for the detection o f gene expression in prokaryotes and eukar y otes. To evaluate its potential for quantita tion of relative promoter activity in E. col i , we have compared GFP with the commonl y used reporter gene la cZ, encoding β -gala c tosidase. We cloned a series of previousl y characterized synthetic E. col ipromoter s into GFP and β -galactosidase reporter ve c tors. Qualitative and quantitative asses s ments of these constructs show that (a) both reporters display similar sensitivities in cells grown on solid or liquid media and (b ) GFP is especially well suited for quantita tion of promoter activity in cells grown on agar. Thus, GFP provides a simple, rapid and sensitive tool for measuring relativ e promoter activity in intact E. col icells .