Expression of Nitrogenase Polypeptides in Yeast

To investigate the expression of nitrogen fixation functions in eukaryotes we transferred nif genes coding for nitrogenase components from Klebsiella pneumoniae into the yeast Saccharomyces cerevisiae. NifH, D and K (encoding respectively the subunit of dinitrogenase reductase and the α and β subunits of dinitrogenase) were not expressed in yeast when introduced as part of the intact nif cluster. Therefore, individual genes were joined to yeast promoter sequences and introduced into yeast in autonomously replicating plasmids. To facilitate the screening of nif gene expression in yeast, the genes were first fused in- phase to a truncated lacZ sequence and subsequently reconstituted.