[Cloning and sequencing of ntrBC genes from Azospirillum brasilense]

A gene library of Azospirillum brasilense Yu62 was constructed in EMBL3. The library was screened with PCR amplified fragment as a special probe. Ten positive plaques (EA1-EA10) were selected. Detection results showed they contained two different types of clones, representing as EA4 and EA9 respectively. Southern hybridization of EA4 displayed that target gene was located in a 2.9kb EcoRI fragment. Sequence of this fragment had allowed the position and identification of ntrC gene, which encoding a protein of 53469, consisted of 480 amino acids. In the upstream of ntrC, a complete ntrB coding region was also found, which encoding a protein of 43487, consisted of 400 amino acids. Homologous analysis of the deduced amino acid sequences of ntrC and ntrB from different bacteria demonstrated that A. brasilense was closer to Rhizobia than to other free-living diazotrophs.