hupS and hupL constitute a transcription unit in the cyanobacterium Nostocsp PCC 73102

The heterocystous cyanobacterium Nostoc sp. PCC 73102 possesses an uptake h ydrogenase encoded by hupS and hupL.. The genes are transcribed in cells gr own under N-2-fixing but not under non-N-2-fixing conditions. We characteri sed the transcription of hupS and hupL in further detail. A transcription s tart site was located at a position 259 bp upstream from the hupS translati on start. As shown by RT-PCR, hnpS and hupL constitute a single transcript in Nostoc sp. PCC 73102. The possible function of short, tandemly repeated repetitive sequences between hupS and hupL, enabling a folding of the entir e intergenic region into a hairpin, is discussed.