Hydrogen uptake in Nostoc sp. strain PCC 73102. Cloning and characterization of a hupSL homologue.

Structural genes encoding an uptake hydrogenase of Nostoc sp. strain PCC 73102 were isolated. From partial libraries of genomic DNA, two clones (pNfo01 and pNfo02) were selected and sequenced, revealing the complete sequence of both a hupS (960 bases) and a hupL (1,593 bases) homologue in Nostoc sp. strain PCC 73102. A comparison between the deduced amino acid sequences of HupS and HupL of Nostoc sp. strain PCC 73102 and Anabaena sp. strain PCC 7120 showed that the HupS proteins are 89% identical and the HupL proteins are 91% identical. However, the noncoding region between the genes in Nostoc sp. strain PCC 73102 (192 bases) is longer than that of Anabaena sp. strain PCC 7120 and of many other microorganisms. Southern hybridizations using DNA from both N2-fixing and non-N2-fixing cells of Nostoc sp. strain PCC 73102 and different probes from within hupL clearly demonstrated that, in contrast to Anabaena sp. strain PCC 7120, there is no rearrangement within hupL of Nostoc sp. strain PCC 73102. Indeed, 6 nucleotides out of 16 within the potential recombination site are different from those of Anabaena sp. strain PCC 7120. Furthermore, we have recently published evidence demonstrating the absence of the bidirectional/reversible hydrogenase in Nostoc sp. strain PCC 73102. The present knowledge, in combination with the unique characteristics, makes Nostoc sp. strain PCC 73102 an interesting candidate for the study of deletion mutants lacking the uptake-type enzyme.