Molecular Cloning and Characterization of a cDNA for theαSubunit of a G Protein from Rice

摘要

We report the isolation of a cDNA for theαsubunit of a G protein from rice (Oryza sativaL. cv. Nipponbare). The cDNA contained an open reading frame that encoded a protein of 380 amino acid residues with a mol wt of 44,204. We designated this polypeptide RGA1 (rice G proteinαsubunit 1). The amino acid sequence of RGA1 was 77%and 86%identical to the sequences of a subunits fromArabidopsis thalianaand tomato (products ofGPA1andTGA1), respectively, and 42%to 69%identical to sequences of mammalianαsubunits. The regions essential for binding to GTP were preserved throughout allαsubunits from higher plants and mammals. However, the C-terminal amino acid sequence, which has been proposed to be a receptor-binding region, of RGA1 was different not only from the analogous sequences of mammalianαsubunits but also from those of the products ofGPA1andTGA1. The mRNA forRGA1, of 1.7 kb in length, was found in the roots and in the etiolated and greening leaves of rice, suggesting that RGA1 might be a protein that is expressed constituti