Study of the Constitutively Active Form of the [alpha] Subunit of Rice Heterotrimeric G Proteins

We used site-directed mutagenesis to engineer two constitutively active forms of the [alpha] subunit of a rice heterotrimeric G protein. The recombinant proteins produced from these novel cDNAs had GTP-binding activity but no GTPase activity. A chimeric gene for a constitutively active form of the [alpha] subunit was introduced into the rice mutant d1, which is defective for the [alpha]-subunit gene. All the transformants essentially showed a wild-type phenotype compared with normal cultivars, although seed sizes were substantially increased and internode lengths also showed some increase.