Figure 1. Physical map of the nif gene cluster in the genome of Azospirillum brasilense (A) and cloning strategy of the nifE promoter region (B). A, Represents the organization of nif and other genes in the chromosome of A. brasilense. Arrows represent the positions and direction of transcription of the operons. The nifENXorf3 orf5fdxAnifQ operon is shown in detail in the lower part of the figure. Each restriction fragment was cloned into the pUC18 plasmid, as described in Table 1. B, Cloning strategy of the nifE promoter region into the pMC1403 plasmid. E, EcoRI; H, HindIII; P, PstI; B, BamHI; S, SalI.