Cloning and sequence analysis of Alcaligenes faecalis nifHDK gene cluster

Total DNA of Alcaligenes faecalis was probed with both the nifH and nifHD sequences from K. pneumoniae. One positive band of about 4.6 kb was discovered. This nifH homologous fragment was cloned into the vector pBluescript SK to construct the recombinant plasmid pBZl. The inserted fragment in pBZl was analyzed by physical mapping and was further subcloned for sequencing. It was found that this A. faecalis nifHDK homology pos-sessed a typical σ54-dependent promoter region with upstream activator sequence (UAS) and A-T rich region. The nifH and nifD ORFs were 888 and 1 476 bp long respectively. The GC contents of these two genes were about 61. 6% and 60.0% . The intergenic regions of nifH-nifD and nifD-nifK were 101 and 105 bp respectively. There were sepa-rate SD sequences upstream of all the three genes. The deduced amino acid sequences of the nifH gene product (the Fe-protein ) and the nifD gene product (the Mo-Fc-protein) were also highly homologous to other nitrogen-fixing bacteria, especially in th