HYDROGEN UPTAKE IN NOSTOC SP. STRAIN PCC-73102 - CLONING AND CHARACTERIZATION OF A HUPSL HOMOLOG

Structural genes encoding an uptake hydrogenase of Nostoc sp. strain P CC 73102 were isolated. From partial libraries of genomic DNA, two clo nes (pNfo01 and pNfo02) were selected and sequenced, revealing the com plete sequence of both a hupS (960 bases) and a hupL (1,593 bases) hom ologue in Nostoc sp. strain PCC 73102. A comparison between the deduce d 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 nonc oding region between the genes in Nostoc sp. strain PCC 73102 (192 bas es) is longer than that of Anabaena sp. strain PCC 7120 and of many ot her microorganism. Southern hybridizations using DNA from both N-2-fix ing and non-N-2-fixing cells of Nostoc sp. strain PCC 73102 and differ ent 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 t he potential recombination site are different from those of Anabaena s p. strain PCC 7120. Furthermore, we have recently published evidence d emonstrating the absence of the bidirectional/reversible hydrogenase i n Nostoc sp. strain PCC 73102. The present knowledge, in combination w ith the unique characteristics, makes Nostoc sp, strain PCC 73102 an i nteresting candidate for the study of deletion mutants lacking the upt ake-type enzyme.