Mammalian Hsp70 and Hsp110 proteins bind to RNA motifs involved in mRNA stability

In this study, in vitro RNA binding by members of the mammalian 70-kDa heat shock protein (Hsp) family was examined. We show that Hsp/Hsc70 and Hsp110 proteins preferentially bound AU-rich RNA in vitro. Inhibition of RNA bind ing by ATP suggested the involvement of the N-terminal ATP-binding domain, By using deletion mutants of Hsp110 protein, a diverged Hsp70 family member , RNA binding was localized to the N-terminal ATP-binding domain of the mol ecule. The C-terminal peptide-binding domain did not bind RNA, but its enga gement by a peptide substrate abrogated RNA binding by the N terminus of th e protein. Interestingly, removal of the C-terminal alpha-helical structure or the alpha-loop domain unique to Hsp110 immediately downstream of the pe ptide-binding domain, but not both, resulted in considerably increased RNA binding as compared with the wild type protein. Finally, a 70 kDa activity was immunoprecipitated from RNA-protein complexes formed in vitro between c ytoplasmic proteins of human lymphocytes and AU-rich RNA. These findings su pport the idea that certain heat shock proteins may act as RNA-binding enti ties in vivo to guide the appropriate folding of RNA substrates for subsequ ent regulatory processes such as mRNA degradation and/or translation.