The kdsA gene of Escherichia coli was sequenced. It consists of 284 codons and is the last gene of a larger transcription unit. The mRNA is terminated by a rho-independent termination signal with the potential to be active in both orientations. This region is followed by another termination signal which seems to be active in the opposite orientation. Upstream of the kdsA gene a second open reading frame (ORF) was found; both this and the kdsA gene are transcribed in the same mRNA molecule when coded from the chromosome. In a plasmid-carried insert transcription starts from a cryptic promoter within the ORF preceding the kdsA gene. This promoter is not active in the intact chromosome.