Expression Analysis of Genes in the Nif Cluster of Clostridium beijerinckii

The nif genes of Clostridium beijerinckii NRRL B593 occupy a region of about 16 kilobases. Besides the two glnB-likegenes, five other genes are interspersed between the nifNB and the nifVw genes. An expression analysis of the nif genes in nitrogen fixing and non-nitrogen-fixing cells with probes generated from various regions of the nif cluster by northern blot analysis revealed the presence of four different transcripts in nitrogen-fixing cells. Two of these transcripts had the predicted sizes spanning fromn if H to nifK and from nifVw to nifVa, respectively. The other two transcripts did not have the expected sizes, but they suggested the presence of two other polycistronic mRNAs consisting of nifE-nifNB and nirJ1-nirJ2-nirD-nirH, respectively. The absence of the nif and nif-associated mRNAs in RNA samples from non-nitrogen-fixing cells indicated that nif-associated genes are regulated in parallel to nif genes.