Organization of the hupDEAB genes within the hydrogenase gene cluster of Anabaena sp. strain PCC7120

A 15-kb DNA fragment containing a cluster of hup genes has been identified and cloned from Anabaena sp. strain PCC7120. These genes are located upstream of the hupL gene in the adjacent fragment in the Anabnena chromosome. Sequence analysis of a 3.5-kb HindIII fragment showed the sequence of hupEAB and a part of the hupD gene, all of which showed high sequence similarity with hyp genes of Escherichia coli and hup genes of several nitrogen-fixing bacteria. These genes are oriented in one direction, as are the hup genes of other organisms. Although the Anabaena hupDEAB genes are in the same cluster as the hypABCDE cluster of E. coli, the relative positions of the genes differ and there is no hupC in Anabaena on either side of hupA or hupB. Unlike several other organisms, hupD and hupE are not closely linked or translationally coupled in Anabaena, but are separated by an intergenic space of 453 bp. RT-PCR analysis of RNA obtained from vegetative cells and heterocysts of Anabaena showed that the hupB gene is expressed only in heterocyst-induced cultures.