BIOCHEMICAL AND IMMUNOLOGICAL CHARACTERIZATION OF RICE HOMOLOGS OF THE HUMAN IMMUNODEFICIENCY VIRUS-1 TAT-BINDING PROTEIN AND SUBUNIT-4 OF HUMAN 26S PROTEASOME SUBUNITS

Previously, we isolated two cDNA clones, TBPOs-1 and TBPOs-2, encoding putative ATPases that are the rice homologues of human immunodeficien cy virus-1 (HIV-1) Tat binding protein-1 and subunit 4 of human 26S pr oteasome. In order to determine the RNA-dependent ATPase activity of t hese putative proteins, the subclones from these cDNA clones were expr essed in Escherichia coli as fusion proteins with maltose-binding prot ein. The recombinant proteins stimulated ATP hydrolysis in the presenc e of poly(U) and rice total RNA. In contrast, single- and double-stran ded forms of HindIII-digested lambda phage DNA are less effective at s timulating ATP hydrolysis, Western blot analysis using antisera agains t the TBPOs proteins showed a widespread appearance of these proteins in rice tissues and cultured cells. The TBPOs proteins were also found around the region where rice proteasomes would sediment. In addition, the TBPOs-1 protein bound to tobacco TATA-binding protein ill vitro. Thus, we suggest that the TBPOs proteins are novel RNA-dependent ATPas es characteristic of DEAD-box proteins and propose that the TPBOs prot eins can exist in rice proteasomes. Further, the TBPOs-1 protein is th ought to play a role in transcriptional events.