DNA fragments from Synechocystis sp. PCC 6803, which act as promoters in E. coli, were cloned by transcriptional gene fusion to galK. They were characterized by determining their relative strength. Shot-gun cloning of Synechocystis DNA fragments resulted in 3% of E. coli transformants possessing cyanobacterial DNA sequences with promoter activity. The determination of relative promoter strengths of 36 randomly selected clones with the galactokinase assay demonstrated the dominance of weak and intermediate promoters.