MOLECULAR-CLONING AND CHARACTERIZATION OF RGA1 ENCODING A G-PROTEIN ALPHA-SUBUNIT FROM RICE (ORYZA-SATIVA L IR-36)

A cDNA clone, RGA1, was isolated by using a GPA1 cDNA clone of Arabido psis thaliana G protein alpha subunit as a probe from a rice (Oryza sa tiva L. IR-36) seedling cDNA library prepared from roots and leaves; S equence analysis of genomic clone reveals that the RGA1 gene has 14 ex ons and 13 introns, and encodes a polypeptide of 380 amino acid residu es with a calculated molecular weight of 44.5 kDa. The encoded protein exhibits a considerable degree of amino acid sequence similarity to a ll the other known G protein alpha subunits. A putative TATA sequence (ATATGA), a potential CAAT box sequence (AGCAATAC), and a cis-acting e lement, CCACGTGG (ABRE), known to be involved in ABA induction are fou nd in the promoter region. The RGA1 protein contains all the consensus regions of G protein alpha subunits except the cysteine residue near the C-terminus for ADP-ribosylation by pertussis toxin. The RGA1 polyp eptide expressed in Escherichia coli was, however, ADP-ribosylated by 10 mu M [adenylate-P-32] NAD and activated cholera toxin. Southern ana lysis indicates that there are no other genes similar to the RGA1 gene in the rice genome Northern analysis reveals that the RGA1 mRNA is 1. 85 kb long and expressed in vegetative tissues, including leaves and r oots, and that its expression is regulated by light.