MOLECULAR-CLONING AND CHARACTERIZATION OF A CDNA-ENCODING A SMALL GTP-BINDING PROTEIN RELATED TO MAMMALIAN ADP-RIBOSYLATION FACTOR FROM RICE

A cDNA clone encoding a small GTP-binding protein related to mammalian ADP-ribosylation factors (ARFs) was isolated from a cDNA library of cultured Oryza sativa cells. The cDNA encoded an open reading frame of 181 amino acids, which was highly similar to the ARFs from animals, yeast and Arabidopsis thaliana. The domains that were believed to be involved in the interaction with GTP were remarkably conserved. The estimated rate of amino acid changes in the ARF protein since the divergence of the plant and animal kingdoms was slower than most enzymes examined, but faster than histones H4 and H3, and calmodulin. Southern analysis of rice genomic DNAs suggested two copies of the ARF gene. Northern analysis of total RNA (or poly(A)(+)RNA) showed that ARF genes are highly expressed in young (2-week-old) seedlings, and in seeds at the early developmental stage (0-6 days after pollination), but to a lesser extent in cultured cells.