Cloning and Sequencing of Rhizobium huakuii exoA Gene Encoding a Glucosyl-transferase

From exoR'-11 which could complement two Exo(-) mutants of R. huakuii 107: NA03 and NA10, a 2.0kb BglI fragment was subcloned in pRK415. The resulted plasmid pJB-H701 could restore the Exo(-) phenotype of NA03 and NA10. The complete nucleotide sequence of the fragment was determined, which contains the structural genes of a glucosyl-transferase, as well as the 5'- and 3'- flanking regions. An open reading frame of 984 base pairs was identified as R. huakuii exoA gene. The MW of ExoA, as deduced from the nucleotide sequence, was estimated as 35 kD. Comparison of the nucleotide sequences revealed a high similarity between exoA genes of R. huakuii and R. meliloti. The deduced amino acid sequence of R. huakuii ExoA also showed a high similarity with that of R. meliloti ExoA. Furthermore, the exoA-lacZ transcription fusion gene was constructed and the expression of exoA-lacZ was analyzed.