Abstract: The yigPP4P2 is the smallest known functional fragment of yigP gene in Escherichia coli. We cloned the yigPP4P2 fragment into vector without exogenous promoter. After transferring the new plasmid into JDP14, a yigP gene defect Escherichia coli strain, the normal growth of Escherichia coli was observed. This observation showed that the plasmid played a similar role of the temperaturesensitive plasmid suggesting the plasmid contained intact transcriptional unit. We further verified the transcription products from sequence of this plasmid by RTPCR, suggesting independent ability of transcription. We cloned a series of sub yigPP4P2 fragments with various lengths into promoter probe plasmid pSPZ for blue white screening and βgalactosidase enzyme activity assay. The results showed that pP40V3Z/JM83 and pP40V4Z/JM83 were positive (blue) and βgalactosidase enzyme activity were detected among them as well. Based on these observations, we concluded the promoter of Escherichia coli yigP is located upstream of the yigPP4P2 fragment; and the downstream boundary is located in sequence complementary to primer V4