For bacterial catabolism,transcriptions of catabolic genes were usually regulated in a type of interaction between transcription factors (TFs) and substrates which exhibited an inducible phenotype.However,when genes encoding TFs distanced far away from their target genes,it was usually hard to identify them for the absent of an effective method.In this study,a simple system modified from SIGEX (Substrate Induced Gene Expression Screening) called modified SIGEX was proposed to search catabolic TF genes in genome.Generally,a shot gun screening plasmid pR18GFP which was constructed form pUC18 was used.