Characterization of cDNA encoding for phosphoglucose isomerase of rice (Oryza sativa L.)

Two types of genes (Pgi-a and Pgi-b) encoding phosphoglucose isomerase (PGI; EC 5.3.1.9) were cloned from cDNA libraries of rice cultured cells (Oryza sativa L.). Pgi-a and Pgi-b consisted of 2132 and 2030 nucleotides, respectively. The homology between these genes was 93.0% at nucleotide level. The homology scores between these genes in protein coding region and 3' non-coding region were 95.6% and 79.4%, respectively. PGI proteins encoded by Pgi-a and Pgi-b consisted of 567 and 568 amino acid, respectively, sharing 95.8% homology at amino acid sequences. Of 11 PGI genes from other plant species and organisms whose amino acid sequences had been determined, a dicotyledonous plant Clarkia lewisii PGI showed the highest homology (about 80%) with rice PGIs. GC contents at the third position of rice PGI genes were about 40%. In order to confirm the enzyme activity of the protein encoded by the rice cDNA, Pgi-a was subcloned into an expression vector, pBluescript II SKp, which was introduced into Escherichia coli. The transformant had an additional PGI activity from Pgi-a.