The rubella virus RNA binding activity of human calreticulin is localized to the N-terminal domain

The rubella virus RNA 3' cis-acting element, which is essential for viral negative-strand RNA synthesis, is specifically bound by autophosphorylated calreticulin. Autophosphorylation in recombinant human calreticulin occurs on serine and threonine residues. The RNA-binding and autophosphorylation activities were localized to the N-terminal 180 amino acids. Furthermore, N-terminal deletions revealed that the RNA-binding activity of calreticulin is abrogated upon deletion of the first 10 residues, whereas the autophosphorylation activity resides between amino acids 60 and 180. These results indicate that both the rubella virus RNA-binding and autophosphorylation activities of calreticulin are present in the N-terminal domain.