Nif promoter of fast-growing rhizobium japonicum

DETAILED DESCRIPTION OF THE INVENTION The taxon Rhizobium japonicum can be split into two groups, fast-growing rhizobia and slow-growing rhizobia or "bradyrhizobia" (Jordan, D.
C.
(1982) Int.
J.
Syst.
Bateriol.
32:136-139).
The structural organization of the nif genes in fast-growing strains differs from that of slow-growing rhizobia in that the nifH and nifDK genes which code for the polypeptides of the nitrogenase complex have been shown to be linked in the fast-growers.
The fix complex is here defined to include all genes involved in the fixation of nitrogen in a Rhizobium japonicum/host plant symbiosis.
The 5'-end of the nifH operon and 5'flanking sequences, including the operon's promoter of the fast-growing Rhizobium japonicum strain USDA191 has been cloned.
Over 4.
2 kilobase pairs (kbp) of DNA were sequenced (FIG.
1).
Sequences encoding nifH and the 5'-end of nifD were identified, as were sequences involved in promoting operon transcription (FIG.
2) and a nifH ribosome binding site.
Seven base pairs (bp) upstream from the ATG translation start site of the R.
japonicum nifH gene (FIG.
1) there is a 5'-AAGGA-3' sequence marking a ribosome binding site (Shine, J.
and Dalgarno, L.
(1974) Proc.
Natl.
Acad.
Sci.
USA71:1342-1346; Stormo, G.
D.
et al.
(1982) Nucl.
Acids Res.
10:2871-2996).
The nifH open reading frame is terminated by a TGA stop codon and encodes a protein having 299 amino acids homologous to the previously dislosed nifH genes.
The area in front of the transcriptional start does not contain any sequences which are reminiscent of typical E.
coli RNA polymerase binding sites (Rosenberg, M.
and D.
Court (1979) Ann.
Rev.
Genet.
13:319-353).
However, the nifHK promoter (a promoter is here defined as the nucleotide sequence upstream from the transcriptional start site containing all the regulatory regions required for transcription) has a sequence 5'-TTGGCACG-4bpTTG-3' 89 nucleotides before the translational start site.
(A translational start site is here defined as the ATG-codon translated into a methionine residue at the amino terminus of an open-reading frame and a transcription start site is the first deoxynucleotide to be transcribed into a mRNA sequence