ndhK is a subunit of cyanobacteria NDH-1 complex,playing an important role in responding to low CO₂ stress.Its expression level is induced by low CO₂ and high light.To further understand the mechanism of transcriptional regulation of ndhK with light,we find the TSP(transcription start position) with 5′-RACE(Rapid Amplification of cDNA Ends),forecast that ndhK contain four possible promoter,construct a series of promoter probe vectors containing eYFP (enhanced yellow fluorescent protein) and use western blot to detect them.The results showed that the upstream sequence of ndhK in Synechocystis sp.PCC6803 containing four sequences (-374 to -274，-438 to -374，-604 to -543，+1 to +52) which can promote gene expression and one can inhibit (-543 to -440).