THE ESCHERICHIA-COLI STPA GENE IS TRANSIENTLY EXPRESSED DURING GROWTHIN RICH MEDIUM AND IS INDUCED IN MINIMAL MEDIUM AND BY STRESS CONDITIONS

The transcriptional regulation of the stpA gene, encoding the Escheric hia coli H-NS-like protein StpA, has been studied as a function of a v ariety of environmental conditions, and its response to trans-acting f actors has been characterized, Chromosomally located stpA is expressed primarily from a promoter immediately upstream of the gene which is s everely repressed by the homologous nucleoid-associated protein H-NS. However, we show here that even in a strain containing functional H-NS , stpA is transiently induced during growth of a batch culture in rich medium, It can also be induced strongly by osmotic shock and, to a le sser extent, by an increase in growth temperature, Moreover, when cell s are grown in minimal medium, we observe a more sustained induction o f stpA which is dependent on the leucine-responsive regulatory protein (Lrp). This enhanced level of stpA transcription is virtually abolish ed in an H-NS-independent manner when the culture undergoes carbon sta rvation. A sensitivity of the stpA promoter to DNA topology may contri bute to some of these responses, Results reported here show that clone d fragments of the stpA promoter region can confer H-NS and Lrp respon siveness upon a lacZ reporter gene and suggest that several hundred ba se pairs of DNA upstream of the transcriptional start may be required for regulation by these two proteins.