IDENTIFICATION OF CDNA CLONES FOR RICE HOMOLOGS OF THE HUMAN IMMUNODEFICIENCY VIRUS-1 TAT-BINDING PROTEIN AND SUBUNIT-4 OF HUMAN 26S-PROTEASE (PROTEASOME)

We isolated two rice cDNA clones, TBPOs-1 and TBPOs-2, which share an impressively high identity to human immunodeficiency virus-1 (HIV-1) Tat binding protein-1 (75% identity) and subunit 4 of human 26S protease (76% identity). These rice cDNA molecules contain domains for putative ATPase and RNA helicase (DEAD box) activities. We propose that TBPOs-1 and TBPOs-2 are the rice homologs of HIV-1 Tat binding protein-1 and subunit 4 of human 26S protease, respectively and are members of a novel family of putative ATPases in plants. Northern blot analysis revealed RNA transcripts for TBPOs-1 and TBPOs-2 in rapidly proliferating rice cells and in younger seedlings of rice. In Southern blot analysis, TBPOs-1 and TBPOs-2 probes hybridized with homologous sequences in genomic DNA from rice and Arabidopsis, suggesting that these genes are widely conserved in the genomes of higher plants.