Objective To thoroughly characterize the P ylb promoter and identify the elements that affect the promoter activity. Result The sequences flanking the − 35 and − 10 box of the P ylb promoter were divided into six segments, and six random-scanning mutant promoter libraries fused to an enhanced green fluorescent protein EGFP were made and analyzed by flow cytometry. Our results showed that the four nucleotides flanking the − 35...