ISOLATION OF CDNAS ENCODING GUANINE-NUCLEOTIDE-BINDING PROTEIN BETA-SUBUNIT HOMOLOGS FROM MAIZE (ZGB1) AND ARABIDOPSIS (AGB1)

We have isolated cDNAs from maize (ZGB1) and Arabidopsis (AGB1) encodi ng proteins homologous to beta subunits of guanine nucleotide-binding protein (G protein). The predicted ZGB1 and AGB1 gene products are 76% identical to each other and 41% or more identical to animal G protein beta subunits. Both predicted proteins contain sevenrepeats of the so -called ''WD-40'' motif, where WD is Trp-Asp. RNA blot analysis indica tes that ZGB1 mRNA is present in the root, leaf, and tassel and that A GB1 mRNA is expressed in the root, leaf, and flower. DNA blot hybridiz ations indicate that maize and Arabidopsis genomes contain no other ge nes that are highly similar to ZGB1 and AGB1, respectively, suggesting that the newly isolated G protein beta-subunit homologues are likely to have unique functions. Furthermore, these G protein beta-subunit ho mologues are conserved among other plant species and may play importan t role(s) in plant signaling.