DOUBLE-STRANDED-RNA-DEPENDENT PROTEIN-KINASE AND TAR RNA-BINDING PROTEIN FORM HOMODIMERS AND HETERODIMERS IN-VIVO

The yeast two-hybrid system and far-Western protein blot analysis were used to demonstrate dimerization of human double-stranded RNA (dsRNA) -dependent protein kinase (PKR) in vivo and in vitro. A catalytically inactive mutant of PKR with a single amino acid substitution (K296R) w as found to dimerize in vive, and a mutant with a deletion of the cata lytic domain of PKR retained the ability to dimerize. In contrast, del etion of the two dsRNA-binding motifs in the N-terminal regulatory dom ain of PKR abolished dimerization. In vitro dimerization of the dsRNA- binding domain required the presence of dsRNA. These results suggest t hat the binding of dsRNA by PKR is necessary for dimerization. The mam malian dsRNA-binding protein TRBP, originally identified on the basis of its ability to bind the transactivation region (TAR) of human immun odeficiency virus RNA, also dimerized with itself and with PKR in the yeast assay. Taken together, these results suggest that complexes cons isting of different combinations of dsRNA-binding proteins may exist i n vivo. Such complexes could mediate differential effects on gene expr ession and control of cell growth.