Organization of nifH and nifD genes in Nostoc commune UTEX 584

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Virginia Polytechnic Institute and State University


Nostoc commune UTEX 584 is a photosynthetic desiccation-tolerant cyanobacterium capable of fixing nitrogen. Biotinylated nifH and nifD gene probes from Azotobacter vinelandii (a gift from Dr. Dennis Dean) hybridized to nifH and nifD sequences isolated from Nostoc commune UTEX 584. This result supports the view that the nitrogenase structural proteins and their genes are highly conserved in nitrogen-fixing organisms (Rice et al., 1980). Southern transfers of genomic DNA prepared from N- commune UTEX 584 were digested with Hind III and hybridized with nifH-specific and nifD-specific probes. Multiple copies of nifH (three) and nifD (two) were detected. Using colony hybridization, a recombinant N- commune UTEX 584 genomic DNA-pBR322 plasmid library was screened with the biotinylated nifH-specific probe and positive hybridizing nifH clones were isolated. A restriction map of the 3.5 kb Hind III insert of the recombinant plasmid (pND001) was produced. From partial sequencing data it was possible to determine the positions of the N. commune UTEX 584 nifH and nifD genes within the cloned fragment and compare the partial nucleotide sequence and deduced amino acid sequences of the E- commune UTEX 584 nifHD genes with other organisms. Isolation of the nifH and nifD genes from Nostoc commune UTEX 584 now permits a more detailed study of nif gene expression in this desiccation-tolerant photosynthetic microorganism.