The hupSL encoding uptake hydrogenase of the N2-fixing cyanobacterium Anabaena siamensis was cloned and sequenced. Anabaena siamensis hupS and hupL contained 963 and 1,596 bp, respectively. The predicted gene products for hupS and hupL consisted of 320 amino acids with a molecular mass of 35,436 Da and 531 amino acids with a molecular mass of 60,704 Da, respectively. Their deduced amino acid sequences showed higher than 90% and 88% similarity for HupS and HupL respectively, compared to those of other cyanobacteria including non N2-fixing cyanobacteria. The intergenic 195-bp sequence between hupS and hupL showed no homology to others among cyanobacteria but it still contained the repetitive sequence, which could form a hairpin structure commonly found in other N2-fixing cyanobacteria. RT-PCR analysis showed higher transcription level of hupS and hupL in Anabaena siamensis grown in BG110 under anaerobic conditions. Nickel exogenously added to the culture was also found to increase hupL transcript.
