The glnA mRNA, encoding glutamine synthetase, is differentially accumulated in the cyanobacterium Synechococcus sp. strain PCC 7942 in media containing different nitrogen sources. With the different nitrogen compounds, transcription of glnA initiated at a single site located -146 nucleotides upstream of the translation start site of the gene. A similarity of the nif-like promoter of the glnA gene of Anabaena sp. strain PCC 7120 and a binding-site sequence for the Synechococcus sp. strain PCC 7942 transcription regulator, NtcA, were found upstream of the transcription initiation site.