Characterization of DRGs, developmentally regulated GTP-binding proteins, from pea and Arabidopsis

Developmentally regulated GTP-binding proteins (DRGs) from animals and fungi are highly conserved but have no known function. Here we characterize DRGs from pea (PsDRG) and Arabidopsis (AtDRG). Amino acid sequences of AtDRG and PsDRG were 90% identical to each other and about 65% identical to human DRG. Genomic Southern blotting indicated that AtDRG and PsDRG probably are single-copy genes. PsDRG mRNA accumulated preferentially in growing organs (root apices, growing axillary buds and elongating stems) compared with their non-growing counterparts. At DRG mRNA was relatively abundant in Arabidopsis leaves, stems and siliques, less abundant in flowers and flower buds, and barely detectable in roots. Histone mRNAs are known to accumulate predominantly during S phase of the cell cycle and are markers for proliferating cells. The patterns of histone H2A mRNA accumulation in pea and Arabidopsis organs were very similar to those of DRG mRNAs. An antiserum raised against a PsDRG N-terminal fusion protein recognized 43 and 45 kDa proteins. PsDRG proteins were more abundant in growing pea roots and stems than in non-growing organs, but they were equally abundant in growing and dormant axillary buds. After differential centrifugation, PsDRG proteins were found primarily in the microsomal (150,000 x g pellet) and soluble (150,000 x g supernatant) cell fractions.