NIFV IS CONTIGUOUS TO NIFHDK IN FRANKIA STRAIN FAC1

The organization of genes with the capacity to code for four proteins involved in nitrogen fixation in Frankia strain FaCl was determined by restriction fragment mapping and nucleotide sequence analysis. Analys is of the 44-kb genomic cosmid clone pFAH1, isolated from a cosmid lib rary made from Frankia strain FaC1,resulted in the identification of a 7.2-kb PstI fragment to which Klebsiella nifH, nifD and nifK probes h ybridized. This nif-hybridizing fragment was subcloned and analyzed by restriction fragment mapping. Further subcloning of the 7.2-kb fragme nt and subsequent sequence analysis of approximately 6.8 kb revealed t he presence of six open reading frames (ORFs). Four of these ORFs have the potential to code for nifV-, nifH-, nifD- and nifK-like gene prod ucts and the two others are unidentified ORFs. The organization of the structural genes for nitrogenase is the same in this Frankia strain a s it is in most other nitrogen-fixing prokaryotes, but the positioning of the nifV-like gene relative to the nifHDK cluster differs. A conse nsus nif-promoter-like sequence, found 5' to nifH, was not detected up stream of the nifV-like gene. Nine copies of a 7-bp direct repeat were found 5' to ORFA.